Hi Baltanong,
Why do you need a rackmount? If you want realistic orchestral scoring capabilities, you definitely need more than one module. The K2600 is a great sounding synth and it's ROM is okay. It will *not* compete with some of the orchestral sample libraries available today for realism unless you add RAM to it (I don't think that you need the sample option unless you want to do your own sampling if I'm not mistaken). It's strength is VAST and that's useful for synth sounds. Recreating realistic orchestral sounds is not its forte.
It all depends on how real you want it to sound and how much money you have. IMHO, Gigastudio with a fast PC (you can get a rackmount PC by the way) and a couple of large hard drives will give you the best, most inexpensive results. Other than that, you would need a few K2600R's or a few Emu samplers to get a realistic orchestral reproduction.
Put it this way, the Miroslav Vitous Orchestral library comes on 5 CD's (approx. 3.25 GB), the Peter Siedlaczek Advanced Orchestra sample library comes on 8 CD's including the Upgrade set (that's 5.2 GB). The Kirk Hunter Strings - 5 CD's alone for just the String section.
There is a reason why Hans Zimmer has a wall full of samplers to create his virtual orchestra. It's because he needs to. You have not given anyone a budget here that you want to work with or exactly what you'll be doing for your orchestral scoring (ie how realistic you need it).
Personally, the Virtuoso 2000, I find weak too, especially it's strings. It's difficult to get a good representation in only 64 MB of space (the Virtuoso2K has 2 Roms in it). oh well, I've gone on too much here.
If you're scoring simply in studio or at home, the K2600R is a better choice than the Virt-2K. There may be better alternatives for you though.
HTH,
fv