I'm a complete newbie to the world of synths and midi. My background is in "classical" music composition, concert recording engineer and electronic/desktop publishing.

I'm looking to buy a good synth that can approximate the sound of a full orchestra. Money is not a big issue and I want to get something I won't outgrow in six months or a year.

My question, finally, is that looking at the raw specs, the Equinox Pro seems to be better than the
K2500/K2600. However, it doesn't seem to have the widespread support that I might need if I get into trouble.

Any thoughts would be appreciated.

I really dont know much about Equinox, but I am a K2500 user. The internal orchestral sounds are great and realistic sounding. There are also a vast library of sounds available for the Kurzweil on floppy and CD-Rom. The Kurzweil is not something you will outgrow. The only minor setback may be the issue with polyphony. I believe Equinox has 64 note polyphony, the K2500 has 48. But one needs to understand how the K synths work when it comes to layering keymaps. For example, one layer of strings on a K sounds great, you may not have to use multi-layering to get a great sound. You could eat up polyphony by using 3 layers of strings for example.

Yep, I have to agree with Chris regarding the K25. It truly is a powerful machine and because of the architecture, may take you a while to get used to.
Now days, 48 voices doesn't sound like much, but as Chris alluded to, a single layer will go a long way especially when you add in a couple of the other oscillators that do not subtract from the overall polyphony.
I am also unfamiliar with the Equinox, so all I can suggest is that you try to spend a great deal of time with each synth before you make your final decision. While the factory sounds on the K25 are really pretty good, they can be a whole lot better once you start digging deep into the synth.