A decent sequencer (be it hardware, or software) will play back multi tracked sequences no problem.
Bad news is:
The D-50 can handle two parts at most.
It's more a dedicated synth than a do everything unit.
There was a device that you could add to a D-50 that made it mutli-tambral.
However if I where you I would look for something more up to date, and current.
There's also the D-5/10/20 keyboards, which are multitambral, but the D-50 has a more powerful sounds thanks to it's effect processor.
I use my D-50 mainly for master keyboard duities, modules do the rest...
With the money your looking at you should find somehting brand new that will suit your needs.
------------------
The Sonic Energy Authority - a sound investment
_________________________
The Sonic Energy Authority - a sound investment