OK, I've had my fair share of things to say about XACT and the XACT GUI in the past (just ask Scott Selfon), but seriously... just make a better version of FMOD Designer? FMOD Designer is inferior to the XACT GUI in just about every way. Possibly except stability.
WWISE, on the other hand... that's a different matter.
Pandemonium, an occasionally updated blog about my game, XNA, games development, and the games industry;
XapParse, a parser for XAP (XACT) files