Hello, my favorite audio interface would be the RME products, in production studios many use the UFX, Fireface, Multiface, Babyface etc. I just love the Babyface in my home studio, really great audio representation, flexibility, mobility so for me it works out great. There are a number of great systems out there (I've own and tried most) but from experience for mixing & mastering, getting the best in your budget is very important! It's obvious (If engineering is important) having the best, for me has given years of awesome service, and I can hear every detail. If your audio/interface has an internal problem, I can see your predicament but if you have to have to go into "Preferences" to reload your interface, I'm sure you know the "Start-up" procedure? Like turning on the A/I and other midi devices first before starting Sonar? Please forgive me if this sounds dumb? but it can happen, like if everything is running and then you turn off the A/I you'll get a disconnection warning? If it shuts down or disconnects with every interface, then you will have to look into your computer (Bios, Device manager etc.) if it just started, look into any "Windows Update" even some Virus Protection (if a recent change or update has been done) might see Sonar or one of it's plug-ins as "Hidden Objects" and might ask you to Quarantine or Delete? This might break a connection path or other? The members on this forum are very knowledgeable and always ready to help, good luck. 

RME whatever.
 
Determine your pricepoint and interface (FW, MADI, USB, etc.) and get the best RME Model you can.
When you are buying an interface, above all you are buying DRIVERS! RME has rock-solid drivers. New companies who otherwise specialize in preamps, midi gear, etc. can throw features into a box, but not guarantee that they will be stable and continue development. I like Presonus as a company, but I have an audio interface from them that is in a box, as they never continued development in a Win7 world. 
 
I've used a Fireface 800 for years. Quality preamps. Relatively high end conversion. Professional low jitter clocking. Analog plus ADAT/SPDIF digital connections. Flexible software routing. Everything just works!
 
If that's more than you need, the FF400 is actually an improvement.
Babyface, UFX, etc...
 
Can't go wrong!

I bought an RME UFX and have never regretted buying it. It's expensive but i wanted something that would handle pretty much anything i would ever wanna do. Its Rock Solid! I'll probably never own a different interface!
I asked the very same question on this forum a while back and RME came up the most. I'm very glad i listened!
They have all price ranges and i wouldnt be afraid of any of them!

Hi Marvin, sorry to hear that you are having a hard time with your 8i6.  Please contact Focusrite support via this link: http://us.focusrite.com/answerbase/contact

Jim and Matt are the tech sperts, I'd go that route first.
RME UFX is a great interface, as many have already stated.
 
T

You may not have to buy a new interface.
 
Is your interface the only one?
 
Sometimes Sonar will look for the first driver in the registry. Goto:
 
HKEY_LOCAL_MACHINE\SOFTWARE\ASIO
 
If your interface is not the first one, rename the other folders in the left pane until the one you want is first in line. Just put a z or something in front of the name already there. ie: ASIOPodXT. Rename that to ZASIOPodXT. It won't affect your other sound devices.
 
If your looking for something better. RME or Roland's Capture series.
 
Good luck!

Just an additional tip: don't open the Focusrite Mix Control applet while SONAR is already running.  That's the only time my 18i6 has ever become magically disconnected, so I simply don't do that.   Otherwise, the interface + drivers has been very solid for me.
 

+1 for RME. Works great for me while having problems with various other brands --- won't buy anything else any more.

I agree with what Jim said above - chances are your interface is not the issue, however if you are truly set on buying a new interface - I also have the RME UFX and would highly recommend it.  But you would be best served by confirming you have no issues iwth your core system, as connecting any interface to an unstable system will just cause you further headaches.
 

RME Firface 800 has worked good for me. But I haven't had any problems with the Edirol FA-66 either.

However, if your computer is having problems a new interface may not be the answer. I just throw that out there because it would suck for you to invest in a new interface and find out your problems are not resolved. If you live in the Toledo, Ohio area you can borrow my Edirol.