Hmm, youre talking about 2 great synths so this will be alittle difficult.
I own K2500XS with all of the upgrades and am very happy with it. Its strengths are the sound quality, flexibility with editing sampling and sequencing. It has a powerful multi effects processor known as KDFX. The power of the sampler and sample RAM can give you virtually any sound you want. If its not in the ROM programs, there is a infinite library of sounds and samples you can purchase, download from the internet. Plus the power of VAST gives you the ability to use the ROM to create your own programs and the possibilities are endless. The K2500 has built in SCSI connections, 8 outputs and fiber optic coax output. K2500 can read Akai, .wav, ROland and Ensoniq.
Now for the downsides. Its expensive, not only for the synth but the upgrades. Also many say that the 48 note polyphony is a small set back. I dont find this to be a major issue, some, however do.
Basically the Triton has similar qualities to the K2500, it is less expensive, but I find the programs(like you had mentioned) to be weak, repetitive and extremely midrange.
Triton DOES have 64 note polyphony and also a built in vocoder and sampler. I played around with its sample mode and found its editing features to be quite limited. I dont own the Triton but I have heard many positive aspects of it which once again are similar to Kurzweil.
You should play around with both synths and make the decision for yourself. You can come to a conclusion much faster by getting the hands on experience. Good Luck.