Well, I reflashed the board to the latest BIOS, which surprisingly opened up some additional memory config options. Apparently its a fix for what became a known issue.
Funny thing happened next: Still wouldn't recognize memory on its own in channel 2...but Windows and BIOS would both see the memory in channel 2, and that was new. So I got it to register all 6 gigs as long as one stick was in channel 1. But this was with all memory independent...no dual channel, even...which is strange.
So I then just stuck the channel 1 stick into the last slot in channel 2 and hard rebooted...and it restarted itself twice, with an additional beep, and then booted up fine in triple channel on channel 2.
Success!!! ...if totally wierd and random.
Thanks for the assistance, guys.