I've just seen your writeup on UT2004, some very interesting findings there. I've been fiddling with this game for years trying to get the best possible sound out of it and you are the first I see mentioning this DirectSound dependancy of the game. Until now, I've been under the impression that it's just OpenAL, so it shouldn't have any problems under Win7.
My current setup is an Audigy 2 ZS with CMSS+headphone mode, system driver unchecked, official drivers. By and large, this setup works ok, but there's some issues that led me to believe something is up with it - with EAX on, sound is completely broken in some specific maps. DM-Goliath is the one that comes to mind right now, but there are a few others as well. Basically the positioning is completely off, nearby sounds are almost completely muted. After reading your page I've tested it with ALchemy and system driver checked, and while I can confirm that the game indeed reacts to it, on this card the result isn't entirely positive - there were now pops and and sounds cutting off all over the place, but I did test Goliath as well and it seems that the aforementioned positioning issues are gone at least. I did try a couple different ALchemy settings, but nothing really helped fixing the issues.
I also have an X-Fi Titanium lying around that I briefly tested a while back with system driver unchecked, with this card I was getting symptoms much like the ones you described on your page, however at the time I put this down to my Z68X-UD7-B3 board using a non-bypassable PCIe bridge chip. It seems like it may well be down due to the game itself though, considering you got the same results, but why does system driver unchecked work more-or-less fine with an Audigy, but not the X-Fi? Might be because the game was originally designed for the Audigy. When I get around to it I'll retest the game with the Titanium card and ALchemy. Why checking system driver seems to cause it to use DirectSound is beyond me though, could be that the included AL .dlls in the game folder are a wrapper of some kind, while unchecking it causes the game to go straight to the openal32.dll in the Windows folder?
I really wonder if there are any more OpenAL games that have more to them - it always seemed bizarre to me that lots of these were included in the ALchemy compatibility list, but now I see there may be good reasons for that. Some other recent testing of mine includes Doom 3 and Quake 4; the former tends to exhibit some sort of strange screen twitch whenever EAX is enabled, and I've not yet figured out if Surround or Stereo is the correct setting for CMSS headphone usage, however I couldn't make out any difference between the two. For the latter, what I could tell was sounds were cutting out a lot, but I guess it's expected on an Audigy since the game was designed for the X-Fi and probably requires its 128 voices.