Does anyone have any opinions on this synth? I'm trying to decide between this and the Alesis QS8. Can't find too much info on the Roland AP-90EX.

The correct name of the master controller is Roland A-90EX not AP-90EX.

There's a lot of information on the net, including http://www.rolandus.com

If you have a specific question, I have an A-90 but I don't know the QS-8.

I happen to own an A-90EX and I generally am very happy with it. However, I find it to have a very slow response when playing block-style piano chords. This is true both for the internal sound module and external modules. It seems to scan the whole chord before transmitting/playing the first note. While this might not bother everybody, it is very irritating for heavy jazz piano playing. I'd say that it's worth checking out the other options if you are a big chord player. However, I LOVE all the illuminated buttons and the attendant possibilities of sculpting patches as you play. It is truly a versatile machine, and as long as you don't primarily see it as an electronic piano, you should be happy with it. Oh, and another thing... It's bloody heavy ! Do you like lugging dead weight to gigs ?