If you want "realistic" piano and sting sounds, then Kurzweil is about the only choice. While I have not played the 88mx, I currently use a PC2x and a K2500Rack. Having played every other major brand keyboard out there, nothing is better.
For all the other sounds (synth, pads, horns, organ, etc) I use the Korg Triton Pro which is also available in a Rack and has a sequencer/sampler built in.
That being said, the "VSampler" technology can get really close to those Kurzweil sounds. It definitely cheaper than a K2600/K2500 but you will need to buy the "samples" which can run several hundred for like a piano set. Check out
http://www.sonicimplants.com there is a huge selection in many formats.. VSampler uses the "SoundFont" format I believe. The cool thing is it allows you to have a software synth on your computer since it uses many samples assigned to key ranges (like the Kurzweil keymaps) rather than "generating" the sound on the fly which takes a lot of compute power. I have considered using that on a laptop and just a Midi keyboard as a easy way to play those 45min sets without having to haul all my gear.
I still use the Cakewalk products for recording and editing - Sonar V3.1 has everything I have ever needed to produce a professional quality CD. I generally record all the keyboard tracks in the Midi domain and then send them to my sound sources and capture the audio when I have all the "stumbles" taken care of. Also of note, it comes with VSampler that I mentioned above and you can generate scores if needed. When all that is done, I bring in the other players and capture their audio tracks then spend time mixing it all down to a final 2-track mix.
There are many new plugins in the sonar product that make all of the above easy and flexible.
Hope that helps,
MZr7