well, Workstation keyboard synths tend to have the most sounds...
things like the Korg M3, M50, Triton series (extreme, studio, TR, LE)...
as for effects, the kaoss products are the only real stereo effect devices that KORG make... but you can only have one simultaneous effect...
there are synthesizers and workstations, like the M3, that have built in effects.
the
M3 has 5 insert effects, two master effects, and one total effect (that isn't the number of different effects it has, but the number of slots that you can load any effect in to). the
M50 has the same but you won't be able to sample or send external sounds through it.
The
Radias (keyboard or just the module) has 8 insert effects and one total effect. I've always thought it would make a great stereo effect processor, but a little complicated for most users.
the other thing to ask yourself is, are you really going to use all that?
workstations tend to be kind of costly, most being at least £1000 if not more here (brand new, anyway), the M50 starts in the £800 range, as does the
TR...
You might also want to check out the
X50 and
MicroX, as they are 'affordable' spin offs of the triton range, effectively being almost identical to the TR and
LE.
you can't use them for effect processing though.
if you're prepared to dive in the deep end, something like the
Radias or cheaper
R3 gives you plenty of effects processing, plus the ability to actually use it for effect processing, plus they are complete synthesizers, meaning you can make your own sounds from scratch - no need to use the presets. in fact, that is the main purpose of synthesizers, to create new, unheard before sounds. but there are many parameters involved in creating those sounds... its kind of an art in itself, but immensely powerful in the right hands. you could easily argue that with the ability to create your own sounds, you don't need to go through thousands of presets to find what you want.
or maybe you're just looking for something like the
KP3?