Mark -- I'm not expecting to be too into 3-D effects, so I'll plan on using the Debian drivers for the video.
Thanks for the tip about ASUS, I'll look at their motherboards for my preferred CPU. The Gigabyte does indeed have a large number of USB 2 ports (8 on the back panel, with support for up to 4 more from the front panel). Right now I don't even own any USB 3 peripherals; I'm interested / willing to get a motherboard with USB 3 support basically as a hedge against future developments, since I'd like this computer to stay usable for some years, and can't predict what the future of port standards will be. Thanks again for all your help, -PT
