Roland MIDI on 7-strings?
There are some people that will string up a guitar with nothing but thin strings and just use the guitar as a controller. I use the Yamaha G1D, G50 and Korg N1R. I use the G50 so I can control any Synth module. Utilizing a Korg TRITON Rackmount through the G50 is absolutely amazing. It makes the rolands look like a 286 chip compared to twin ghz computer. But back to the point, a 7-string output would require a totally different hardware interface. Using a peizo bridge/ MIDI controller, you could sum the MIDI to a mono-interface and use all 7 strings. The problem though is that it is mono and you lose all of the hexaphonic capability. There are some company's that have a onboard convertor that terminate to a 5-pin MIDI as opposed to the 14 pin hexaphonic output. The Parker MIDI fly comes to mind. Also check out the iGuitars from Brian Moore. They have a 7-string guitar with MIDI ouput that terminates to a 5-pin MIDI interface. The 7-string is MIDI is possible, just not through the roland 14 pin interface. good luck.