Credit to "Geoff" for this post - read it for a summary of the error. Seems I'm not the only one who runs into strange errors.
Naturally, this error is a real bitch. Windows fails to tell you WHICH audio device changed, making it a trial-and-error approach to debugging. I hate that, as they could have easily mentioned which device was causing the offense.
Plus it takes about an hour to re-create the error, making troubleshooting very slow.
For my part, here is what did NOT fix the error:
1. Disabling Windows driver signing enforcement. My Hauppage WinTV-PVR-150 cards were listed as "Sound" devices in Device Manager, making them (possibly) "audio" devices to Windows. They had yellow exclamation points in Device Manager only because the drivers are not signed for Windows 7. So they worked, but they could have run into some kind of driver checking BS that caused the error sporiadically.
However, turning off the driver checking using the F8 Windows boot menu did not help.
(To be fair, Microsoft would not have classified the TV capture cards as "Sound and media devices". Hauppauge probably did that.)
Still, if you are troubleshooting this error, it makes sense to check to see what other devices may be in your PC under "Sound" devices, besides the actual sound card you know about.
2. Disabling the unused Nvidia HDMI audio outputs. Long shot, I know.
3. Re-updating the Realtek audio drivers. The drivers were the latest anyway, but reinstalling did not help. Another long shot that did not pay off.
4. I have tried the registry trick to disable automatic Windows detection of audio devices. It did not work.
5. I tried ticking "PCI lock" as suggested here. However, the Hauppauge drivers did not automatically reinstall from Windows Update, so perhaps this method does not actually apply to Win7 x64. Reinstalling the original drivers does not seem to have fixed the audio device error/crash, but it did seem to (temporarily) fix the yellow (!) marks on the WinTV-PVR-150 cards in Device Manager.
6. I tried plugging in the headphones. The usual notifications and such popped up, but Media Player did not puke. So it is not because the system is detecting the headphones being plugged in incorrectly.
7. I tried "logging" the PC with CamStudio, which is a screen recording application. It captured the WMP error with both the audio devices panel and the Device Manager open. The WinTV 150 cards did not display any errors, and the Realtek audio devices did not show any changes that would indicate a transient error. So it seems the Hauppauge cards are not the issue. The Realtek could still be dropping out momentarily, too fast for Windows to recognize and re-display.
I did not try codec packs. This is a brand-new Win7 x64 machine and I refuse to believe it does not come with codecs for DivX / Xvid and MP3 audio. I do not pollute my machines with unnecessary crap. The files play fine until the error, indicating it is not a codec problem.
Next stop is to quit BeyondTV and see if I can replicate the error. If I can, the WinTV-PVR-150 cards and extra Nvidia video card will have to come out. The video card is unnecessary anyway, as I cannot duplicate my desktop on the built-in Intel video and the external Nvidia Geforce anyway.
If the error still persists, I will have to assume it is a defective mainboard, and try to get it replaced. (If true, it would be the first time I have identified a new mainboard as defective, and I have been doing PCs for nearly two decades.)
At least it does not seem like I have to replace the WinTV-PVR-150s. I would, if it would fix the issue, but I would not like to because I do not think there is anything wrong with them. I hate replacing stuff just because, but will happily spend $150 on a new dual-tuner card if it fixes this damn issue.
Brother, what a lot of work this new PVR is! If you want to build one, do yourself a favor and just get new everything. Recycling old hardware to Win7 seems to be a losing proposition these days with all the driver issues.