I disagree now about the Bontempi 666 range being unbendable. I've had mine for a week and although I'm yet to bend it, I'm already experiencing random glitches happening with the sound selector buttons and the on/off buttons. The Bontempi BT-605 has some major bugs in it and it is very easy to mess up the sounds and operation of the entire keyboard just by switching it on, then off multiple times in combination with pressing buttons and starting the demo, rhythms, etc.
So far, just by randomly pressing the buttons on the Bontempi, I have managed to get the keyboard to glitch and malfunction with around 9 different and repeatable bends. Also, there are some unpredictable glitches that occur with the power on and off buttons and sometimes you get a loud scream from the speaker or a long, continuous and full volume organ sound when switching it on. On one occasion I managed to get a low-volume sound that was like a continuous matrix scan, or random arpeggiator noise that was very, very fast and partially musical. It reminded me of the bug on the Hing Hon when you press down multiple instrument buttons and it cycles through them all in like a super-fast arpeggio.
If the Bontempi can glitch and malfunction just by pressing its buttons alone, I can imagine just what could be achieved once I get in there and really have a good go at it.
*edit: I'm thinking that some of the bends in a Bontempi might also need to be wired up at a button level... because with these strange button combinations, it might be possible to attach pots and components to control whatever it is that is happening here.