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
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
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