Well, I guess I have GBS, also. Most likely there IS a drug for it, or at the very least, a lawyer willing to sue because of it.
I also had the same problem with the computer freezing up. I also stream music and all that other fancy jive your not supposed to do. Just like you, I NEVER do anything while Mach is cutting. I did uninstall everything not related to mach, trying to resolve the situation, however, it persisted anyway. I did manage to figure out the problem ONLY happened after I plugged in a USB stick. It might not happen for 5 minutes, or it might not happen at all, but one thing was for sure, it would NEVER freeze up if I didn't insert a USB stick. If I do have to transfer some files via USB, I reboot after I use it, and it runs purdy as a fluffy kitten. Now I can listen to my tunes, and use Mach, with a lower amount of anxiety over doing so. Dunno if this helps you any, but it was worth a try. I'm not disagreeing with what BR549 said though, it's not really a good idea to use your computer for anything other than Mach.