A tremolo on a variax 300?. The smallest surface mount tremolo and least intrusive to your Variax 300 that I know about is the $100 Bigsby B5, which would be a tight fit, however that's not the problem. For the existing piezo pickup bridge setup to work, the strings must pass through the body to create a positive piezo pickup to string contact. So if you could successfully mount the B5 to the 300, you still might run into pickup trouble when passing the strings over the back of the 300's bridge plate flange and under the B5's tailpiece roller, resulting in poor piezo/string contact. Where there's a lot of will, there's a way, and most likely at your expense. The Variax 300 VDI (J45) cable connection to a MIDI synth ?. I do not know of a 3rd party interface device. The signal that passes through the VDI (J45) cable to and from your Variax and other line 6 enabled devices most likely use their own unique digital communications protocol. Unless your an electronics guru and hacker extraordinaire, you might be out of luck. keep searching and maybe some helpful information could turn up. I myself, would be very interested in harnessing those capabilities if its possible.