Unfortunately as far as I am aware vArranger is for PC only so would not be suitable for the OP.
Your best bet is
Ableton for live play or
Cubase or
Logic for a studio base all of which can host VST Plug-Ins.
You will also need an arranger with good Midi Control facilities which in order of sophistication are: Bohm, Wersi (OAS 5 and above), Korg, Roland & Yamaha. (Not sure about Ketron)
In addition depending on what you want to do, a good Midi controller keyboard can be used instead.
Hope this helps
Bill
_________________________
English Riviera:
Live entertainment, Real Ale, Great Scenery, Great Beaches, why would anyone want to live anywhere else (I�m definitely staying put).