How did you have your drivers setup in Sonar?   I installed the lastest drivers 1.8, and am still getting audio drop outs (512 samples ASIO) or 10ms WDM/KS

I'm even get drop outs at 1024 samples in ASIO, even worse than MME at 20 ms

I 
 

musicroom

AT
USB is probably best for long term.
 
I'm enjoying the Tascam uh-7000 in for evaluation at the moment.  Nice bit of kit.  I haven't messed w/ it much, but the DA is a semi step above my normal TC Konnekt, which has very good DA. 
 
@

 
AT, Let us know how it sounds with outboard pre's attached if you don't mind. This box has my interest...
 
 
Thanks

The Tascam unit has preamps and line ins.  The manual is pdf and I haven't double-checked but I think they bypass preamp itself.  You can download the manual at Tascam, I believe.  Anyway, I've run the warm audio preamp/WA76 combo through it and it... worked very nicely, thank you.  And the portico II, too.  The converters are a notch above my TC Konnekt unit, from what I can tell.  Listening to a song I had been working on, the first thing I thought was to add more reverb to the vocal, since I could hear .... deeper?  And the DA of the TC is very good.  The difference isn't jaw dropping as so many like to say, but it seems to be there.  And the preamps themselves are great.  Not as vintage as the WA stuff, not as big as Mr. Neve's  stuff, but as good as either just different.  All this is very subtle stuff.  But the Tascam unit is first class, however you cut it.
 
@

Kroneborge
I'm even get drop outs at 1024 samples in ASIO, even worse than MME at 20 ms

This may or may not help you, but (using only ASIO) I keep the sample rate at 48,000 on my Focusrite as well as whatever audio software I use. I've noticed (especially in Standalone mode for audio software), if the sample rate don't match, I get error messages/no sound.
I haven't had any issues with Sonar, but you may just need to verify your sample rate settings for the 6i6 and Sonar are matching.   

My computer is a i7 -4830 with 24 gigs of ram.  And most of my tracks are bounced down right now (probably still not more than 20 audio tracks).  
 
I will play with it more tonight.  Note that I am changing latency in the asio panel, not the normal mix slider.  And it changes it in samples.  Note normal latency slider is grayed out for me.

screen shot of my setup, still a no go.  
 
https://www.dropbox.com/s/kqzahebiazztw1u/Screenshot%202014-07-09%2019.04.49.png
 
 

Uninstall ASIO4All from your system. It will interfere with the native drivers for your hardware.
For lack of a better word, it is very "aggressive" and Sonar will find it before it finds the real ASIO drivers for your interface.
Once you are using the Focusrite drivers, you should see the performance the others are.

W

Cactus Music
Well that must be the classic "a picture is worth a 1000 words"
What Bob said.. holy cow ASIO4all... Kill the bastard. 
You'll be fine once you get rid of ASIO4all. 
I was wondering why you had a slider in Sonar, once you get the scarllet drivers installed you can only change those settings in mix control. 

LOL!!
I was also surprised to see the ASIO4all driver being used, especially with such good drivers from Focusrite. I remember using ASIO4all in a general purpose laptop just to "rig" it so I could listen to some X1 audio (it of course didn't have an audio interface). I would only use those drivers if there was no other legitimate driver available.