Well, the SK20 definitely can pull off greater things than what was in those things posted above. That unit is all about combining the different outputs and the different sections in creative ways. I love mine to bits, although it usually indeed takes some work to get nice sounds out of it. In fact, that buzzy / plastic low-register sound heard on those demos is exactly what I personally try to avoid with the SK20 (well, reverb + delay + overdriven preamp works in that regard as a remedy).
These guys are using it also for actual music too, you know: http://www.youtube.com/watch?v=uJ5RPMiAoyA
It doesn't differ that much from the sounds from this one either (although that one allegedly has 2 VCOs in the synth section): http://www.youtube.com/watch?v=aDK5iERs ... re=related
To original poster: perhaps I didn't quite understand why you feel motivated to buy the Delta, but on some level it almost seems irrational to me (and many others it seems). The Trident is a quite hefty and a sought-after synth, although in that sense I guess if you really can get a decent sum for it, it could be worth selling. However, technically speaking it's really in an entirely different league than any string machine -type of unit. Do you understand the limitations a paraphonic keyboard (like The Delta & SK20) are going to have compared to a proper polysynth? They can be pretty annoying to play due to the single filter design, although like stated above that can be fun sometimes - that is, in the recording setting, not
really when playing live. The SK20 is pretty nice in this respect though as it allows you to continue playing notes on the "string" section, even if the synth's filter would have already closed due to earlier notes having been played - but it's far from perfect this way either.
If you need a gigging synth though, I don't see why it couldn't be a VA / sampler as you're already using one too and see no problems with it. Lugging a 70s synth around is never without its own risks. I doubt the Delta would be that much an improvement sonically over the SK20 if it would be functional though (well if the envelope on the synth section is indeed busted, then you're basically missing most everything that synth is capable of). But if you will manage to find a Delta and still prefer it over the Trident, then obviously you have made the right choice in the end. It's still a pretty considerable downgrade in technical terms, really.