If you play an accoustic guitar on a Tyros it is played like a guitar is played and not just as you push the keys.
Well, most synths are 'good' in many domains, but they usually 'shine' in one or few. This is the case for both the Tyros & new Kurzweil. If you're looking for a synth with 88 piano keys, good 'natural' instrument and those 'mega voices' Kara is referring too, than you definetly must have a look to Yamaha's S 90 ES. Also a beautifull and great sounding piano-synth. It's not a workstation though, so if you're into sequencing you need to look elsewhere. It does play midi files though, so it's a great instrument for on the stage and great for the studio as master keyboard.
Btw... personnaly, I think that hardware synths still have an edge over their software brothers... OK, they're more expensive too, so don't start this discussion...
Moon