Sounds like you want a workstation/arranger more so then a synth. Anyhow you said synth, and your looking at Korgs...so at the very least I would say check out The MS2000 from Korg ( stand alone or the rack mount ). Also im not a big fan of the Tritons ( for mostly subjective reasons )...one of those I have an unhealthy love for the Trintity.

Might want to look into some Alesis...ION is lots of fun ( no risk of getting bored after a day ). Check the micron as well.

The karma...perhaps you might want to look into some Nords.

Random I know..