Sorry I forgot to reply to this - I've been pretty busy with MA work since September - I just managed to get the original DJX keyboard for a steal of £20 from a second hand store in Newport, (thankyou newport junky scene! I will feed your habits) I've seen some vids of bends on youtube for this keyboard which seem interesting but the quality is pretty gash.
To electrolyd: I'm guessing you got this far but once you have the DJX-2B open, you will see a square section covered by a screw-fastened chunky bit of steel, you need to remove this. You should now have exposed the interesting parts of the circuit board (outside of this are just amp circuits and variable resistors connected to multiplexors I think, I didn't find much there). The large rectangular chip on the left (with the machine face down) is the one that I hacked - there is only one large rectangular chip as far as I remember, it had a barcode and yamaha printed on it on mine that I removed for some reason. All of my switches are connected to one pin, that is then short-circuited to a number of the others - I did this using some vero-board to create a basic matrix. The secret if at all is that you need to use a small signal diode for every switch (these are directional and I can't remember which way round, you'll have to test). If you don't use any diodes, the machine will crash, and if you just use one diode on the main pin it will crash everytime you throw more than one switch (using my method anyway).
The main pin I am referring to on the chip is the 2nd on the bottom right hand side (if the keyboard is face down with the x-fader towards you) Or one of the ones either side, but I pretty sure it is that one. You will have to test which pins you can connect it to - it is quite a few but some do still cause crashing.
However the bends do not work with all the backing loops and things the unit has to offer - sometimes they will just cut the sound out and you will have to reset etc.
Also, try plugging a midi capable keyboard into the machine to discover a load of new sounds!!
Don't worry about the QY-10, i found plenty of bends but I can't hack soldering to surface mount chips, it was just painful!!
Psycho:Active: The unit only has inbuilt sounds, the CD is just connected to a weird rotary sensor thing which makes scratch sounds and plays beats - sorta cool in a gimicky way as is everything else on the machine.
I will find the photo's of the inside of the toy to elaborate on this!