Hi all,
I ordered the Roland Mobile UA and I am VERY happy. Thanks very much to Leandro Duarte for the recommendation.
It offers 4 independent channels recognized by Pianoteq and working (tested with headphones). As I only have two speakers connected right now, I tested playability in a two channel setup. Very impressive, to my ears no discernible latency at 256 samples. I test latency by having the Casio's internal system playing in parallel to the MIDI-Pianoteq sound. This is not a numerical measurement, but if I can't distinguish two different sounds on a keystroke I figure it will not affect my playing at all. I can hear a slight latency at 512 samples.
So: sleek package not larger than an mobile phone, easy setup, great sound, minimal latency, 4 channels, for €100 -> this is a very clear recommendation.
The only downside is that it is just out of production, I've picked it up on eBay.
Best wishes
Andreas