Okay, I've finally settled on something. I decided to pass on the ASRock box. The price was just too high for my liking, and I've ordered a Zotac ZBOX HD-ID11. Yes, it's going to have a dirty proprietary NVIDIA graphics chipset. The interwebs tell me that it's the only one that will do H.264 decoding in hardware. I'm not sure I particularly care, for my application.
It comes with DVI and HDMI, and a DVI-to-VGA dongle, so I should still be able to plug it into whatever floats my boat. What I did did just realise, about 15 minutes after I placed the order and was changing Zoe's diaper, was that I don't have a remote control solution now. The ASRock box included a remote control.
I figure I can use one of the 6 USB ports and get some sort of USB infra-red adapter, and probably keep using the Hauppauge remote that came with my PVR-350 card.
With the money I've saved buying the ZBOX, I've ordered a 40Gb Intel SSD, so that should make for a nice, no-moving-parts front end (assuming everything works).
Everything should arrive before Thanksgiving, so I'll have a few days off work to tinker.
Here's hoping I haven't bought a lemon.