well, I think I'll end up getting an Audigy 2. Couple of reasons why:
1) Used Audigy 2 can be found for cheaper than a new or used mystique or montego DDL.
2) Audigy 2 does support up to EAX 4 (although I have yet to find anyone who even notices what EAX 4 does).
3) CPU usage w/ Audigy 2 is slightly lower than Mystique 7.1
I've survived w/o 5.1 in my games so far, so I'll probably be able to survive for a while longer until I can pick up a nice klipsch 5.1 setup. Anyway, thanks everyone for the input.
edit:
4) I know everyone hates Creative and their drivers, but I get the impression the Mystique developers have the same problems. So why not go with what will be supported more often, the Audigy.