Hi Guy's
First the FX150 is quite astonishing it's rated at 150w with a 6.5" dual cone speaker.
I've been using a Helicon Singthing for quite sometime now which is a FX150 with the built-in Harmoniser so I knew what the amp was capable of when I bought it. You can also pair the two together for more power if needed.
The Korg microkey connection is an A to B USB cable (printer cable) I used to use a KMA and I've always felt comfortable with the small keys.
montunoman: In response to your request I've just recorded a quick number to try the harmoniser be interesting what you think, it's a bit weak in the middle eight but it was a quick effort. It's also the first time I've used the recorder on the SD40. I just normalised the track using Audacity and converted it to an MP3 file.
https://app.box.com/s/ikmfqqfpbn2nafbbl0lssua9tjr7ffcwRegards, Col