Etostone, I think I have your solution. The problem is the onboard audio's drivers, not TASCAM's.
 
As I said I've never had a need to switch between consumer and pro programs, but I know the TASCAM drivers are solid so I thought your blaming their drivers was probably wrong. I got my clue when you said you had satisfactory results with a bogus ASIO driver. That means it was tasking the Windows driver among multiple devices. Another clue was when you said you had another computer with the M-Audio card. If you're using a different computer, then there are MANY more differences other than just the audio interface you're using.
 
So try the following. Go into Device Manager and turn off all audio drivers that aren't TASCAM, like this:
 

 
Once I did that, SONAR used the TASCAM's ASIO driver, and Windows used the TASCAM's WDM driver because Windows was no longer confused about which driver it should use. In fact I was able to play back from SONAR, listen to YouTube via Chrome, and play music from my internal music library via Windows Media Player all at the same time. I could stop and start any of them any time, adjust their levels independently, etc. etc. It was quite the interesting mashup.
 
With regard to your concern that there haven't been any updates since December, maybe the reason why there haven't been any updates in the past eight weeks is because the drivers don't have a problem.
 
lludwick, I don't have any sources for recording into the interface here, but FYI the 48V (and unlike some interfaces, I measured it and it's within 10% - I've measured as low as +34V from some interfaces) affects only the XLR connectors. However, I don't know if this is an issue but you should NOT plug a 1/4" plug and XLR into the same input. Just because there are two jacks in the same input doesn't mean you can use them. The manual is explicit about this.
 
I'm 99.999999999% sure the problem you're having involves setup somewhere along the line. The TASCAM US-4x4 and 2x2 have been rock-solid for me, and the hardware is pretty bulletproof so it's probably either a misapplication of the 4x4 or something misset in SONAR.
 

Just as an update, I am doing test projects to adjust the settings of the 4x4 dials to give me the levels I am used to working with from my previous Tascam interface. Everything is working about right for me on Windows 7 Pro.
 
The only weird glitch I'm having is with Sonar reporting it can't find my old US-1641 ports as active. There must be a way to retire older references so that Sonar does not nag me each time I open a project.

Save a copy of the AUD.INI file, then delete it. SONAR will build new entries based on what you're using now. If anything goes wrong, which is extremely unlikely, you'll still have the old one for backup.

Anderton
Save a copy of the AUD.INI file, then delete it. SONAR will build new entries based on what you're using now. If anything goes wrong, which is extremely unlikely, you'll still have the old one for backup.

Thanks Anderton, I had a feeling my old init file was causing the squawking. I will do just as you say, back up AUD.INI as AUD.OLD, then delete AUD.INI, start up again and have a new one built.
 
BTW, I did get everything working this afternoon building little test projects for straight audio recording, Midi recording and VST recording and all works fine. The Tascam 4X4 has a great sound quality that I especially notice on the mic recording side.
 
I am not sure if it is that I use Windows 7 Pro 64 bit, but I have not problems with drivers while I am using the 4X4. I can switch applications and the sound works. Though in Sonar while it is still up, if I switch to my browser for example it will complain that another application is preventing sound. I have always found that easy to live with.

lludwick
BTW, I did get everything working this afternoon building little test projects for straight audio recording, Midi recording and VST recording and all works fine. The Tascam 4X4 has a great sound quality that I especially notice on the mic recording side.

 
I ran tests for the specs and they're pretty impressive.
 

I am not sure if it is that I use Windows 7 Pro 64 bit, but I have not problems with drivers while I am using the 4X4. I can switch applications and the sound works. Though in Sonar while it is still up, if I switch to my browser for example it will complain that another application is preventing sound. I have always found that easy to live with.

If you try what I recommended for Etostone, you probably even won't have to live with that. I certainly find the drivers to perform as expected. I think he's too quick to blame TASCAM rather than Windows audio issues within his computer.

As I said in post #18. I always have disabled on board audio. This good advice was given to me a long time ago on this forum. 
It has always worked for my system. Some systems and on board audio can co exist with ASIO but often there is a the issues as the OP described. So that is always my first recommendation. 
 
And I see no issue with using my "pro studio" playback system for everything. 
I turn most Windows sounds off or at least turn them down in the audio control panel so they don't scare the carp out of me. 
 
I like to listen to finished albums either in Win Amp as an MP# or even play back the CD I just burned in WMP. And I can keep Sonar open and swicth between all of these apps no problem. 
 
BUT!  one disclaimer and it might be the big one. I only work in 44.1. 
I cannot vouch if switching apps works if Sonar is 48 or 96 and Win Amp is trying to play a 44.1 file. 
I seem to remember back when I was using 48 that playing a 44.1 in WMP and on return to Sonar, that Sonar would get messed up and play the song a whole step low. 
 
But anyhow it only takes a minute to disable your on board and see what happens. 
And now we are told to also check for HDMI audio which is messing up a lot of systems lately. 
 
 

Anderton

lludwick
BTW, I did get everything working this afternoon building little test projects for straight audio recording, Midi recording and VST recording and all works fine. The Tascam 4X4 has a great sound quality that I especially notice on the mic recording side.

 
I ran tests for the specs and they're pretty impressive.
 

I am not sure if it is that I use Windows 7 Pro 64 bit, but I have not problems with drivers while I am using the 4X4. I can switch applications and the sound works. Though in Sonar while it is still up, if I switch to my browser for example it will complain that another application is preventing sound. I have always found that easy to live with.

If you try what I recommended for Etostone, you probably even won't have to live with that. I certainly find the drivers to perform as expected. I think he's too quick to blame TASCAM rather than Windows audio issues within his computer.

Anderton , thank you for all your info and investigations about my issue. I appreciate. 
Yes , I have already tried that you mentioned , since I am computer geek , that was one of my first tasks to disable onboard drivers and soundcards. 
Still no effect. I have further issues as I have explained to you. There is no excuse for the system not to shut down properly or not to restart due an audio conflict. That's something about the drivers not working properly on windows 8.1 pro 64 bit. 
Btw, you never told me which is your Os ? win 7 or win 8 ? 
 
I am working fine with the new Asio drivers from this Australian programmer. He did a great job , and gives Tascam much further options ! Yes you should try it really. It has a total free to test drivers. It gives also the possibility to change the audio stereo from left to right channels inside the software , to have only one or two mono outputs very useful for testing your mix before radio mono conversion , giving each program different configuration and to save the profiles and many more. 
 
I wish the solution you mentioned was that easy , but it didn't work for me. I am sure 100 % its Tascam lame drivers. 
But thank you very much again for all the tests and your time.

Cactus Music
As I said in post #18. I always have disabled on board audio. This good advice was given to me a long time ago on this forum. 
It has always worked for my system. Some systems and on board audio can co exist with ASIO but often there is a the issues as the OP described. So that is always my first recommendation. 
 
And I see no issue with using my "pro studio" playback system for everything. 
I turn most Windows sounds off or at least turn them down in the audio control panel so they don't scare the carp out of me. 
 
I like to listen to finished albums either in Win Amp as an MP# or even play back the CD I just burned in WMP. And I can keep Sonar open and swicth between all of these apps no problem. 
 
BUT!  one disclaimer and it might be the big one. I only work in 44.1. 
I cannot vouch if switching apps works if Sonar is 48 or 96 and Win Amp is trying to play a 44.1 file. 
I seem to remember back when I was using 48 that playing a 44.1 in WMP and on return to Sonar, that Sonar would get messed up and play the song a whole step low. 
 
But anyhow it only takes a minute to disable your on board and see what happens. 
And now we are told to also check for HDMI audio which is messing up a lot of systems lately. 
 
 

Thank you Cactus for your detailed info. 
That seems not to be the issue here. As I explained earlier , I have a strong feeling it's still the audio driver supplied by Tascam. It doesn't work fine on windows 8.1 pro 64 bit. All other are disabled. Thanks god this guy from Australia provided those asio drivers, now all seems to work fine so far. 

Etostone
Thanks god this guy from Australia provided those asio drivers, now all seems to work fine so far. 

As I mentioned above, your guy in Australia does not supply an asio driver.  From the manual :
 
"What it is for
Utilising a virtual WDM sound card, this driver allows you to listen or record
windows audio from your ASIO driver. You can make the windows audio appear
as an input into the host application, or monitor windows audio as an ASIO output
bypassing the host application".
 
I'd concentrate on getting things working with the latest tascam asio driver and the latest firmware.
 
 
 

The only weird glitch I'm having is with Sonar reporting it can't find my old US-1641 ports as active. There must be a way to retire older references so that Sonar does not nag me each time I open a project
 
This is something I would like to fix too. I also switched from the us1641 to the Scarlett 6i6 a year ago. 
Any old projects that are opened are looking for the Tascam still. And this is stored with the CWP file as I have re built my computer 2x since the Tascam was hooked up. 
It seems the only way to get rid of it is to do a SAVE AS. and re name the file.