You'll find that most sounds with lots of elements in them are mainly velocity switching and SA type switching elements. So, although they may have 16 elements, or whatever, but fewer than four will sound at any one time. Plus there are a LOT of fancy polyphony algorithms that take a voice that has been used on a quick transient (but the main voice is still sounding) and immediately reassign it to another voice once it has decayed quickly away.

The 9000 suffered extremely poorly in this critical area. It may be time for you to step up to a 21st century arranger

Just take a look at a score for a symphony orchestra, one day. One of the densest, most timbraly diverse things you could ever write for. How many parts are there? Yep.... WAY under 128! Sure, there are a LOT of musicians. But 15 of them are probably playing ONE part (1st violins, e.g.) and this take ONE stereo voice on a keyboard. And take a look at how seldom ALL of them are playing at one time.

Take a listen to a great pop track, or bigband arrangement. Count how many parts there are. They are great not because of how much is going on at one time, but how carefully crafted the little that IS going on is arranged. Read any book on arranging, you'll see the same thing over and over again....

Less is more