Having used Myth for well over a year now it's only recently with the purchase of a new machine have I come across any problems with the VIA chipset. The new nforce board that I've got seems to be behaving itself and machine is stable again.
I started out with a PVR card but I quickly dumped it, well actually sold it on ebay to some chump that paid well over the RRP for it. For me, DVB-T was the way to go. It meant more channels, better picture quality and cheaper hardware. In fact, after spending new years at my parents I'm seriously considering getting a DVB-S card and CA adaptor. The video out on the 350 seemed like a waste of time for me, the old machine would quite happily decode MPEG in software leaving plenty of compute cycles for other things as well.
I'd say try and get it working with your existing motherboard and if things don't work, try swapping the board. My two previous machines worked flawlessly despite having VIA chips.