Good news for your two Zunes... something I did recently fixed mine.
A new update was apparently just released both for the PC and the Zune firmware. Unfortunately, I'm not sure that was what fixed it because I was in the middle of trying another fix.
So if the firmware update still doesn't fix your Zune's, try this other thing I did:
1. drained the Zune's battery completely
2. plugged it back in to a rear USB port and keep it plugged in until fully charged (battery indicator green)
3. as soon as it regained a wee bit of life while charging, I wiped the whole thing with the key combination (
http://support.microsoft.com/kb/927001) and reinstalled the fresh firmware
Once it was fully charged, I put my content back on and then left it running the whole night on repeat playing one of my ripped CDs that used to crash it a lot. I have also tried playing the radio a good bit (it used to crash a lot during this too). So far, it's been solid. So I'm going to tentatively say the problem is fixed.