aspenleaf
I recently went through similar problems when going from Windows 7 to Windows 10 with a Focusrite Scarlett 18i20.  Focusrite's tech support worked with me to solve the problem.  They had me try all their beta drivers and Mix Control software, but nothing worked until I updated the firmware on the interface.  When I initially tried to update the firmware, it kept failing, and tech support couldn't tell me why.  They said they'd had issues when updating the firmware using a Windows computer and wanted me to try it on a Mac, which I don't have.  They wanted me to ship the interface to them so they could update it.  I decided to try using my wife's Windows tablet, and for some reason it worked and after that everything functions fine.  I don't know if there is a firmware update for the 6i6, but it might be worth looking into.

I will contact them to see what they think, thanks.

chuckebaby
are you running the X3 update (X3 E) ?
 
Also make sure to check and see your driver mode is set to ASIO (what you should be running for your Scarlett)
you have the mix control software correct ?
 
this is probably related to your driver problem as I remember a few posts in the past about you having issues with the scarlett drivers.
I would un install and re install them again. make sure your not in a usb3 slot first and for most.
make sure you have a driver supporting windows 10.

yes, x3e.   ASIO yes.   Yes, I had to get a beta driver from Focusrite so that my computer didn't blue screen when I powered down the 6i6.  And yes, reinstalled again, this driver is Win 10 compatible according to Focusrite. 

Wait a moment...what ?
 where are you adjusting the buffer size from ?

chevy playback seems to work ok now on the 1024 buffer setting. But when I go to 512, it starts to glitch again

 You can NOT change buffer settings when in ASIO mode (it becomes greyed out) unless your running in WDM or MME.
mix control is where you change your latency settings. you click on the ASIO button and it opens Mix control.

you use the mix control software instead.
you have physically looked the driver mode and it says ASIO ?
 
https://www.cakewalk.com/Support/Knowledge-Base/2007013007/Audio-Dropouts-Clicks-and-Pops-When-Playing-and-Recording
 

Cakewalk

• Go to Edit > Preferences > Audio - Driver Settings (Options > Audio  > General in legacy products)
• If you are using WDM/KS or MME(32-bit) drivers, try bringing the Buffer Size slider to the right towards "Safe"
• If you are using ASIO drivers, click on the ASIO Panel button. This will launch your sound card's proprietary control panel.

 

chuckebaby
Wait a moment...what ?
 where are you adjusting the buffer size from ?

chevy playback seems to work ok now on the 1024 buffer setting. But when I go to 512, it starts to glitch again

 You can NOT change buffer settings when in ASIO mode (it becomes greyed out) unless your running in WDM or MME.
mix control is where you change your latency settings. you click on the ASIO button and it opens Mix control.
 
you use the mix control software instead.
you have physically looked the driver mode and it says ASIO ?
 
https://www.cakewalk.com/Support/Knowledge-Base/2007013007/Audio-Dropouts-Clicks-and-Pops-When-Playing-and-Recording
 

Cakewalk

• Go to Edit > Preferences > Audio - Driver Settings (Options > Audio  > General in legacy products)
• If you are using WDM/KS or MME(32-bit) drivers, try bringing the Buffer Size slider to the right towards "Safe"
• If you are using ASIO drivers, click on the ASIO Panel button. This will launch your sound card's proprietary control panel.

 Buffer size adjusted in the focusrite ASIO Control Panel box, which can be accessed by clicking the ASIO panel button as well.  i don't understand what you mean you can't change buffer size in ASIO mode...  in the focusrite ASIO Control Panel box.
And yes, the "DRIVER mode" definitely says ASIO, as well as all the other driver id boxes in the different screens. 

And the latest...  was just online with Focusrite support, went over the issue, and told him I downloaded LatenyMon program and ran it, and it seems happy that I should not get audio dropouts.  He suggested I run that pgm while doing playback on Sonar, and try to duplicate the problem.  
Wouldn't you know it...  even at a buffer size of 256, I couldn't get the system to glitch. Sheesh.   For whatever reason, it seems happy now.  Will do more testing...  Will let you now how this unfolds. 
Thanks for all your great support !
 

I know I had a problem with Windows 10 and my (now defunct) echo audio FirewirePre8's I have linked; I was getting pops and drop outs and all sorts of bad stuff; turns out my time clock source settings were wrong and once I fixed those everything went smooth again (very low latency).
 
 

just keep in mind im only trying to help. if your not taking full advantage of the drivers and using some sort of generic ASIO, your losing out on performance the scarlett is supposed to utilize.
however, I still don't understand that buffer size of 256. because Focusrite drivers/mix control are set in Milliseconds.
I use a Focusrite scarlett 18I8 with mix control software.
there is no "ASIO panel" it's called Mix control.
rather than setting a buffer rate like in sonar, your given a latency choice (ASIO buffer size) in Milliseconds.
the !8I8, like mine, uses the same type of drivers/mix conrol as the 616.
 
I hope this helps. that will be my final post. good luck on this issue and happy jamming.
 
Chuck
 

Personally, although i like win 10 for my business, I noticed I can not have the same number of vst's as I use to before the cpu pegs out.  I came from 8, and before that 7.  If I had my way, I'd be at 7 for anything Sonar related.  boy the vst's I could have live in the day... before the "improvements" of Win 8 and WIn 10....
 

chuckebaby
just keep in mind im only trying to help. if your not taking full advantage of the drivers and using some sort of generic ASIO, your losing out on performance the scarlett is supposed to utilize.
however, I still don't understand that buffer size of 256. because Focusrite drivers/mix control are set in Milliseconds.
I use a Focusrite scarlett 18I8 with mix control software.
there is no "ASIO panel" it's called Mix control.
rather than setting a buffer rate like in sonar, your given a latency choice (ASIO buffer size) in Milliseconds.
the !8I8, like mine, uses the same type of drivers/mix conrol as the 616.
 
I hope this helps. that will be my final post. good luck on this issue and happy jamming.
 
Chuck
 

Chuck, I appreciate the help!   I don't know enough about this to know what you're talking about, though...   I don't know what generic ASIO's are...   I just have Sonar X3 Studio and the downloaded "Focusrite Control" software.  That's it.  The mix software is part of that.
But I don't see how we could be operating on 2 different principles.  I have a little icon that looks like a Scarlett interface that's in my toolbox at the bottom of my screen that says "ASIO Control Panel" when I click on it. The panel is black and grey and has the both sample rate and the buffer size displayed, both of which are adjustable. The buffer size goes from 16 to 1024. Must be in bytes. You can access this same box by clicking on the ASIO Panel button in Sonar.