Thank you for your reply, jeneral.
What an interesting solution. That was something that never really came across my mind at all, but it does make sense. The only thing that doesn't jive is the fact that by turning on the NTSC tuner then switch back to ASTC, the digital channels come right back on.
So far, I have tried using an older version of the Hauppauge drivers, and it seems to have solved the problem. But I can't say for certain until I monitor the tuners for a few more days. And if that fails, I'll definitely try adding an additional fan over the mobo, as my case will allow.
As for the 64 bit OS, so far I haven't come across any driver issue. Most of the hardware are pretty well supported these days, I suppose. The reason why I use a 64-bit OS is for the additional RAM. I use video capture software that stores images directly onto RAM before being transferred to the hard drive. The additional memory really helps in that sense. If my pc was only an HTPC, I probably would have just stayed with 32-bit.