For me, my combi of 88 key stagepiano/workstation and 76 key arranger works near perfect... but since moving from the tyros to the pa4x, .. i found that most of my soundcreation stuff works quite well from the pa4x You can do almost anything you want with the pa4x synth and sound part in the same way a workstation does.. except for synth arpeggiator

If you want/need more then 3 sounds layered, you could reroute your midi out to the midi in, then create an empty style, and choose 8 more sounds from your style tracks... you could even use multipads on top of that for doing some arpegio like things and drums...

You could also choose to use the ipad as a midirouter, and add some ipad stuff to your sound... but this is not necessarilly needed.