Some of the EXes appear to use the standard Serial port, some hardware is controlled via the joystick ports (GVP G-Lock for example).
The AG5700 would need a Serial Port EX, and it's possible that it might be compatible with some generic VCR EX - the problem is, none of the EXes supplied with Scala are for VCR control, so I doubt they'd have the necessary control types like FF, RW, cue to counter etc.
I'll try loading some of the others and see what they offer.
The only VCR control I've found is the Scala Echo, but that is a Sony LANC controller (that I don't have) and it's not clear whether that uses the serial port in a standard way, or if it bit-bashes the protocol (which I assume would be less likely to work in an emulator, where I'd like to run it).
