Ah, no hard feelings. Just a little sad. And yes, you have been very unlucky.
I have been thinking ...
You'll remember that back then (the time of your tweeters) Dogber admitted that his drivers didn't do something right (must have been
this topic). I don't know whether you still use his driver, but now look at this :
Vista acts strange regarding the
change of Exclusive Mode. You can check this yourself a little by unticking those two checkboxes in the Advanced tab of the device properties. ... from here on, the device will be always in use until you perform a reboot. Now :
XMPlay also acts strange regarding Exclusive Mode, and it can play in Shared Mode even if you don't want it (ask for it). E.g. my FireFace can play in Shared Mode only (XMPlay).
Then, XX acts strange regarding Exclusive Mode, because it *cannot* play in Shared Mode (anymore).
These both latter could be enough to let Vista choke at forcing it into a mode it officially can't (but which is wrong, see the checkbox test). If I sneakily add to that a driver which is not 100% following Vista's rules (and again, if you still use Dogber's driver that certainly won't do that for its good cause), we're all asking for trouble. I'd say, read that topic I just referred to, and you'll know what I mean, and how easy it is to blame a player (which would be both XX and XMPlay at that time).
So it is the combination, and no occasional coincidence. In your no-boot case, I bet that the status XMPlay left the whole WASAPI thing in, didn't match what XX makes of it, with Vista in between being wrong in the first place. Again, this is sufficient to not call it a coincidence.
That the system can get into a state of not wanting to boot anymore, is kind of logic to me, although I would never be able to explain it (I just don't know enough about it). I once followed a trojan being active, and how the OS fights against that. You really won't believe what all happens when the OS misses something (senses that it can't do something), and what it is going to install, uninstall, activate, deactivate, in order to recover. Thousands of happenings (and the trojan wins) which can go wrong by themselves, and if then the system dies, it can well be in a state of not being able to reboot.