Sorry, but likewise for the keyboard amps... (OK, not gutless, but still anything but flat).
About the only way to hear your arranger without coloring the sound unacceptably are either studio monitors or a GOOD home hi-fi system for home use, and good quality (which doesn't NECESSARILY mean expensive!) PA speakers - powered or unpowered is fine.
Basically, if you hear a noticeable difference in response between a good stereo system or studio monitors, and whatever you are currently playing through, you aren't hearing your arranger in all it's glory... and neither is your audience.
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An arranger is just a tool. What matters is what you build with it..!