This one was bought (also) from ebay and still is a beloved piece of equipment! I love it so much and have it beside my bed so I can play a note or two before falling asleep. Have played a lot with it using an external keyboard (an X-Board 49 from EMU) where I have set many voice parameters to its knobs. So you can play with attack/release, cutoff/resonance chorus/reverb, mono/poly/portamento etc. It gets very interesting when you remove the attacks from pianos and plucked instruments and instantly turn them into distant reverb-filled pads.
There is this guy that has some info on which controllers map to which attributes and there is a plan on the back of my head to make a controller for specific parameters of the QY using the MIDIBOX. (www.ucapps.de)
QY is a real jewel and made me love freezepop.