Is any of this useful in diagnosing a Sonar freeze problem?  This is what Windows gives me:
 
Description:
  A problem caused this program to stop interacting with Windows.

Problem signature:
  Problem Event Name:    AppHangB1
  Application Name:    SONARPLT.exe
  Application Version:    21.13.0.32
  Application Timestamp:    56c1f66a
  Hang Signature:    7dea
  Hang Type:    0
  OS Version:    6.1.7601.2.1.0.256.48
  Locale ID:    1033
  Additional Hang Signature 1:    7dea76717049134cf647bf4855188f85
  Additional Hang Signature 2:    8592
  Additional Hang Signature 3:    859252e609cd61db9465c0b6f7475e3f
  Additional Hang Signature 4:    7dea
  Additional Hang Signature 5:    7dea76717049134cf647bf4855188f85
  Additional Hang Signature 6:    8592
  Additional Hang Signature 7:    859252e609cd61db9465c0b6f7475e3f
 
I suspect I'm getting hangs because of my work method on this project, and am going to try and rebuild the song a couple of ways to see if the problem persists.  It could also be my Mackie Onyx 1620 driver, or sound card, which is showing signs of wear. But first things first...if anyone can read that gibberish above and perhaps know immediately what it means.

Unfortunately, to the best of my knowledge Windows usually has no way of knowing the cause of a hang. All it knows is that an application has taken too long (> 5 seconds) to dispatch a Windows message. It can identify the application, but that's all. What exactly caused the application to get stuck is known only to the application.
 
In fact, Windows doesn't even know if the app is really hung or just taking a long time to perform some operation. A "true" hang is when the software is waiting for something to happen that isn't going to ever happen, such as an infinite loop. More often, it's waiting for something to happen outside the program such as a response from a device that's broken, shut down or disabled.
 
"Hang signatures" are a relatively recent thing, new (I think) at Windows 7. I have not found a good explanation as to what they really are, other than a way to indicate whether the hang you're getting today is exactly the same as the one you got yesterday. I don't think there is any useful information in them beyond that.
 
As for troubleshooting, it's a hit-and-miss process, starting with the most likely suspects: hardware and hardware drivers. I think you're right to place the audio interface at the top of the suspect list, although it could also be the USB port it connects through. Hopefully, the hangs are frequent. If so, you could try disconnecting the Onyx and enabling your motherboard's integrated audio while playing back a bunch of projects.

Problem went away by turning the computer on first, then the mixer.
The Mackie Onyx 1620 mixer with the Firewire Card apparently likes to go second.
Everything is now rock solid.