Hello Hans --
There is some disagreement over the word "workstation". (I don't get involved in those discussions. :-) ) However, Derek made a good point: "Use whatever feels right for whatever you want to do." This means thinking and reflecting about one's musical goals, needs and process (i.e., what do you want to achieve and how?) Then it comes down to finding best tool -- arranger or synth -- to accomplish your goals.
I avoid discussion about the word "workstation" because each keyboard has its own features and supported workflows. The Montage/MODX sequencer is kind of rudimentary (performance record) while the Genso/Tyros/PSR sequencer supports deeper MIDI editing. Of course, PC-based software can do all of that and more.
My church side is interested in orchestral music. I play an MOX live in a small group (piano plus guitar plus me). The Montage/MODX orchestral instruments are quite good and I plan to upgrade to MODX for live play. Its light weight is a big plus for playing out.
However, I also feel that the Genos orchestral instruments are stellar. I have used Genos as a synth at my church gig, too, although it is a much bigger hassle to port to the gig. The Genos and Montage/MODX orchstral instruments are both based on the same waveforms, but I feel that the Genos programming, especially, SArt2, is superior for live playing.
I prefer PSR/Genos for DAW-based sequencing. Maybe it's because I'm familiar with the XG sound architecture over the MOX architecture. Montage, apparently, has some changes that were a step back from the Motif/MOX DAW integration. I sequence to produce backing tracks for my funk, R&B, and jazz side.
So, even though the Genos has so many advantages, I still plan to upgrade to MODX. I have to haul my instrument to the gig (and rehearsals), so transportation and set-up/tear-down time are important.
BTW, Blake Angelos' MODX demo for Guitar Center touches on building an orchestral layer. Some mighty fine orchestral instruments are hiding in the MODX, but that isn't what sells keyboards to the masses these days. ;-)
Hope this helps -- pj
Music technology blog:
http://sandsoftwaresound.net/