Pretty new to all this still, but when I record my guitar amp using a Sennheiser mic into the front panel of my 8i6, I am getting a clear signal. I then record into an audio track and it does grab the signal; however, at playback it sounds super distorted, garbled, etc...like a broken speaker.
 
I am on 44.1MHz and have 10ms buffer set on the 8i6.  What should my Preferences be set to in SONAR?  It sees the 8i6  and is defaulting to 44.1MHz, and the latency is set to 10ms.
 
But still...bad playback.

Welcome to the forum.
What Driver Mode are you using?

I think you mean 44.1KHz.
 
Depending on the power of your computer, 10ms might be a bit too much for it to handle.

I am using WDMD/KS.  When I change things, the software does a scan and comes back all happy.  As for my system, it's a dual i7 with 16GB.  The spindle I run from is a SSD, and I have a GEForce GT 640 card.

Go to the Focusrite web site and download/install the latest drivers for the 8i6 and your operating system, if you haven't done that already.
Then try the ASIO driver.

While there are a lot of factors that could cause audio quality issues, Greg mentioned two of the first things to check: making sure you are using the latest drivers and using the ASIO driver mode in Sonar.  If those do not help, there are some Windows settings outlined in this article that can have an effect:
For Win7:
http://us.focusrite.com/answerbase/optimising-your-pc-for-audio-on-windows-7
For Win8:
http://us.focusrite.com/answerbase/optimising-your-pc-for-audio-on-windows-8
 
If you continue to have issues it could be a DPC latency problem.  For more on DPC latency:
 
http://www.thesycon.de/deu/latency_check.shtml
 
If you continue to have trouble after trying the above, please contact Focusrite support using this link:
 
http://us.focusrite.com/answerbase/contact

I get garbled playback from time to time - like blown speakers all fuzzy and distorted - and have to restart Sonar when that happens.  But, I am talking about playback of existing tracks which were already recorded successfully.