In your other thread you mentioned that you wouldn't be performing the backing tracks live.
If that's the case then my other suggestion stands. Get a good quality MIDI controller and invest in some good software synths and sequencers.
Or there's also the option of going with a good MIDI controller and hooking it up to a synth rack module.
You can pick up some really choice used modules for a song on eBay or Craigslist and put the whole setup together for less than $700 to $800 but you'd sound like you were running and $2000 rig.
Take a look at the Korg M3M Rack or Korg TR Rack or any of the Yamaha Motif Racks or even a Roland Rack and see what they're selling for used these days.
Or for something more modern look at the Waldorf Blofeld Desktop Module.
A setup like that, with a rack module or two would work on stage as reliably as any hardware setup for about half the price or less.
Gary