Nick, since you are happy with the DisCover5..and know the instrument..I would suggest you move up to the G70...Everything you love on the DisCover5 is on the G70...but improved...
In the USA, you can find clean used G70's under $2,000..making the G70 a great buy..

As you know Roland still owns the field in SMF play/edit...and the G70 continues that and more...

You mentioned the Audya....as an arranger, if you can allocate that much money...will sound great...SMF's on past Ketron's don't compete with Roland..(in my opinion)..

Overall bang for the dollar without compromise..G70..

For the best sounding arranger..Audya..