I've experienced the VIA bug and my system did not have a hard lockup. I had to rmmod then insmod the ivtv kernel modules or reboot to get it working again.

I am not entirely sure what fixed the problem, but I disabled the onboard video, printer port, updated the BIOS to the latest as of over a year ago, and bumped the RAM up to 768MB.
It has been rock solid for over a year and a half now. Just upgraded the HD to 300GB yesterday and did a fresh install of R5A26.
so far, so good.

What about the cache directory settings? These I believe are in mythtv-setup.

Considering the amount of hardware changes you've made, and still are experiencing the same problem I would take a look at the settings in mythtv-setup. I know I have shot myself in the foot with some settings in there.

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