You guys got me curious about these Yamahas, so I got them yesterday. These are not bad, not bad at all. Its been 2 months since I last heard the FXT90 so I don't really remember how they sound exactly, but I'll try to help. Overall they're on the same level.
The Yamahas have less mid bass but more sub bass. Bass quality is equal. So are the mids. The FXT90 treble is forward and is sparkly. The Yamaha treble is not that prominent and the note is kind of quick.
Presentation, the FXT90 is rather forward and aggressive. Yamahas are not aggressive or laid back, right in the middle. Soundstage wise, I'll say that the Yamahas are better. The FXT90 have more depth, but they have the same height, and the Yamahas are wider and the separation is quite a bit better.