I tend to find that self powered PA speakers handle the full range demands of the arranger better than most stage amps, which are often primarily designed to help a keyboardist hear himself through the clutter of a live band's stage sound, hence a bit middle-y and over-present to my ears.

If you want to hear your arranger at it's best, I would recommend a tiny mixer with FX (Behringer or Mackie make good enough ones of those) and hook it to a small Eon, Behringer or Mackie PA powered speaker to keep it cheap, Yorkville or FBT if you've more to spare...

A hair more wiring to do, but add a small powered sub later on, and you've got yourself a pretty decent small PA, there. Start with one speaker, add the other when stereo beckons!