The benefits of the 4 cable method is you can use the high gain mods from rm100 and the clean amps from the hd500 as I do. You can also arrange the effects if you want before or after the preamp.
Iam using the rm100/hd500 together with the four cable method and have great results. Midi works great with the rm100. Midi in from rm100 to midi out/thru on hd500. I read the midi switching on rm100 is set on channel 16 and it work on mine. Once you assign the foot switch to midi, and on...