Well, Matrox has listing specifically for the P4DC6+ as being compatible. The nice thing is they actually show you what the compatible arrangement is (which cards to which slots), OS, firmware, the works.
They also have a listing for my other SuperMicros board (370DDE) as NOT compatible. They seemed to have a pretty good list, growing regularly.
OTOH, Pinnacle has a compatibility list that's gotta be at least a year or two old, never changes, and the closest thing to a "Hard Recommendation" is that LLoyd (their online / forums representation) seems to be pretty fond of one of the Intel 850 MOBOs and Nvidea Video cards. There are some references that include Athlons/Athlon Mobos, but most are looking kinda old (not sure, I'm not an AMD user).
The difference is night and day. Check out the forums, check out the attitudes. I can't honestly tell you how Martox's tech support is, I've never had to use 'em. Pinnacle just kept re-sending the same auto-bot responses, none of which related to the problems I was having. After the third try at contacing someONE in support, I gave up, yanked the board, and got the RT2500 (and I'm living happily-ever-after...)
I'd recommend the the high-end Pinnacle boards, you betcha, right after I suck down a shovelful of warm worms and call the IRS to tell 'em what a great job they're doing.....right after I roll down the hill in a spiked barrel...
I've had some of the other products (firewire cards, nuthin' fancy) and they worked well.
If someone just HAS to have a DV500 or Pro-One, the oft-posted solution (on the Pinnacle forum) is to build the system around the board, or buy a packaged system.
FWIW
Scott