Hi....The MJ works very well with a controller KB like the Roland A37 or any midi connected KB...depending on what the controller features are will relegate how navigation is controlled between the two units & how comfortable you are using it in a performance scenario to make the MJ do what you want to... The MJ is a little less featured as an arranger but has enough to make it play styles with no problem...its weakness lies a bit in its style editing but not something you cant do on a pc if you want to really get in deep.....remember the MJ also has many other super kool useful modes for live play also, SMF, SFX, Wav, Mp3, HD recording, Lyrics, Mic/Vocalizer all in a 7lb unit! Best part, you can play ALL Modes simultaneously also and fade in & out via separately controlled SLIDERS. Styles & Sounds are terrific, in fact I recorded my last CD project using only the MJ. Its easy to get used to the OS, you can load & remove all data via USB also. If your into mixing it up musically & doing it with mucho flexibility in different formats besides just playing the MJ is for you....read more here:
http://www.ketronus.com/midjay.htm