Folks - thank you all for all your help and patience - I now understand where my TASCAM sits in the grand scheme of things, and honestly didn't ever think it actually took the place of the PC sound card... however, really happy to be re-educated and have it explained.
 
Reloading the TASCAM drivers fixed the connectivity problem, and now I understand that the Sound Blaster is redundant, I'll remove it tonight to avoid me, and the PC, getting confused, again. Then I'll focus on getting the ASIO drivers working correctly.... and I may be back again, in a separate post, if I run into problems (which, based on past examples, is almost inevitable).
 
Cheers ... Kimbo
 
 

Just so you know, Sound Blaster ( Creative)  PCI cards have a bad history with Sonar. I speak from experience. I started life 14 years ago with the Audigy II card. It claimed ASIO drivers but it never worked unless I used WDM mode and mostly in MME mode for midi. 
 
The tracks' like you say' were always out of snyc. I gave up on Cakewalk and returned to using my Yamaha MD8 track and my trusty Atari.  Later I joined on to this site to attempt to give Cakewalk a second chance. I eventually bought a M Audio interface but like a fool I left the Creative PCI card installed. I learned later on that Creative PCI cards MUST be removed from your DAW or there will be a conflict.  The M audio was a turd so I bought a Tascam us1641 and switched to a newer PC. I left the Sound Blaster in our office PC where it worked just fine for tunes and movies.
 
With the Tascam and a new PC everything fell into place and thanks to this forum's help I was now recording in ASIO mode and Sonar was my new friend.  The Tascam's original drivers where not that great but over time they have improved immensely and are now very good drivers. The big improvement came out in Dec 2014 when Gibson took over and they started writing there own drivers. 
Alas  looks like they did not upgrade the drivers for your interface  being the last ones are 2010. 
 
http://tascam.com/product/us-122l/downloads/
 
My advice would be to seriously look into a newer interface just to get the better drivers. The US 2x2 replaces yours and they are much improved and not expensive. 
 
http://www.musiciansfriend.com/pro-audio/tascam-us-2x2-usb-audio-interface
 
 

In a hurry here, but check out this thread regarding manual sample offset (picture of where it is entered is first shown in post #4). Also, post #52 has a link to a utility that will do the loop back measurement for you.
 
Bottom line... an interface can have an offset that needs to me accommodated manually (usually a one-time setup), but is good to know what yours is specifically.

Cactus - thanks mate - I'd read about Creative products not being ideal, but I've used them in the past (even though it now appears I needn't have done so) fairly successfully, and they're readily available and reasonably cheap, so....
 
Yeah, my US-122L is a bit old 'n crusty, and it's certainly had it's fair share of use - albeit incorrectly connected it seems (hindsight's a wonderful thing), and I've been considering whether to upgrade to something else, such as US 2x2. However, now I've figured out the correct way to connect and use it, I'll have another go at getting ASIO drivers to work, and hopefully address the latency - if I still get problems, I'll look to upgrade... anyway it's about time I spent a little more cash "productively" rather than investing in my local bar owner's retirement plan.
 
Cheers

Yes the loop back test is always a good idea I'm big on telling everyone to do it. So once you get that done run the loop back test and see if your offset is correct. 
With the Sound Blaster eradicated and every trace of it's drivers and registry removed, then the proper Tascam drivers you might see some improvment
 
Here's a good one I use. Even though it say's Windows 7, it works for me on Windows 8.1.. Cannot vouch for W10. 
 
http://www.oblique-audio.com/free/rtlutility
 
 
 
I also do the manual test where I use a midi drum track, bounce to it audio, ( freeze)  and loop it back to an audio track. 
Zoom in and see if the hits line up. Good idea to check if they drift over time. 
 
Here's my Tascam us1641 running the old drivers:
 
Top track MIDI
Next Track is bounce to audio session drummer- note that it lines up perfectly with the midi.
Next Track is ASIO mode loop back Normal setting for buffer  notice it plays early around 120 ms.
Next Track is ASIO mode loop back highest buffer setting,, no change from the normal setting, so buffers not involved.
Bottom track  WDM mode loop back now it's late by a lot! I'm no longer a fan of WDM mode for overdubs. 

This is what I was suffering so bought the Focusrite.  Which as you see is bang on. I need to re test the Tascam with the new drivers which came out a year after I did this test. 
 

 
 Here' s a few others I tested. The Behringer only has MME drivers. For $30 can't expect much eh! 
 When I look at this I also see how bright and cheery Sonar 8.5 was.. Somebody mentioned codec was not involved with audio but note the output dialog. USB audio codec. The Behringer is a plug and play USB box that works without issue for playback. I use it with my XP and W 7 laptops at gigs because it's one step up from the mini jack on board system. 

 
This is a 2002 PCI card originally used for Radio broadcasting.  Only a 2x2 TRS 1/4" but shows how  PCI cards can be good performers. To bad Creative just plain screwed up with writing proper drivers. My Audigy card is very nifty otherwise with its front panel interface and spdif connections. In a box now as it was only 32 bit so no good on anything new. 
 The company supported it right up to W7 64 bit. It is in my old backup DAW now. And it never caused a conflict with my other ASIO devices. I can just choose one or the other. Note it did not work in WDM mode. 

Am I a happy chappy, or what !!
 
Got home from work, uninstalled all the SoundBlaster software, uninstalled all the odd sound drivers that I'd been messing with, physically removed the Soundblaster card, rebooted. then uninstalled/reinstalled all the TASCAM drivers, just to be sure, and.....
 
OMG !!! Finally able to select ASIO drivers in Sonar, plugged in the mic, hit record, "strummed a couple chords and sang from the heart" (lyric courtesy of Florida Georgia Line) and whammo..... no echo monitoring via the TASCAM, and NO LATENCY on the recording (even stretched to a loud "yeeehhaaa" when that happened) - no nudging, no fiddling, no messing with buffers or settings or anything.... everything syncs up perfectly, straight out of the box so to speak !!!
 
I am honestly as happy as a pig in sh*t !!!!
 
Can't thank you guys enough, finally I can get on being "creative" and not "frustrative".
 

I know this has been solved.  However another +1 for not using SoundBlaster.  I installed a SoundBlaster sound card as the on-board had went out on a motherboard.  After that I kept having Sonar problems and problems with my (at the time) Saffire Pro 40.  I removed the SoundBlaster and the Sonar/Saffire Pro 40 problems all went away.

Regardless of "issues" with SoundBlaster cards, all of my sync problems over the years have come down to two fundamental misunderstandings, of a global nature, which, in hindsight, would've continued to plague me, until now, regardless of what brand of board I'd bought:
 
1) I didn't realize that my TASCAM was actually a "sound card" in a box. I could understand that maybe the "newer" ones are more intelligent, and could do that (but how they did it I had no idea, until now), but mine's kind-of old, so I'd always worked on the assumption that it was nothing more than a clever way to connect things to a PC, kind-of like an external mixer, with a little bit of smarts for signal conversion, and that the USB provided nothing more than power to the device. So, on that basis, it obviously had to be routed via the onboard sound "facility" for it to work (Doh !!). And...
 
2) For some really really unexplainable reason, I hadn't figured out that the basic principles of "USB", and was still working under the impression that it was nothing more than a way of connecting devices to something via a common connector, and which could provide power OR some kind of low-level connectivity for using a mouse/keyboard or downloading photos or backing up files, etc. When in fact, plugging in via USB is pretty much akin to installing a new "board" (of some form) into a "slot" within the PC, anything connected that way actually becomes part of the PC, with all the high speed multi-way comms and power functions that goes with it. Yeah, yeah, I know you're all saying "So which hole has this guy been living in all these years ???".... I wish I could answer that one, and I'm feeling kind of embarrassingly stooopid right now, as a result, but hell, as they say, you learn something new everyday.
 
So, I've have my eureka moment for this month, and will spend a few moment licking my humiliation-wounds, before pressing "record"..... 
 
Thanks to all, once again... Kimbo

Excellent news.
It is a bit confusing because of the terms used. Most people still call their audio interfaces a sound card just out of habit. Back at the turn of the century there was no such animal as USB audio interface. 
USB was to slow I guess. 
PCI cards are ( I think)  all you could buy so the term "sound card" stuck even when they became Firewire or USB.
 
Most on board sound "chips" can co exist with the ASIO drivers of your audio interface. But PCI type cards often take over the system and make life difficult for Sonar. Other audio software might not have an issue but Sonar seems to like a clean house. Most PCI sound cards have simple drivers, but Sound Blaster adds a lot of bloatware etc so is very invasive. 
I don't even install the on board audio drivers when I build my DAW. I have no problem playing any type files, even u-tubes and Windows Media player stuff.. Some people like to use the on board for windows stuff, but me I like my clean house for my DAW.