Well, I'm not sure what you are trying to do but I tried a few things on my 740, and like the DGX it will only play slash chords in the accompaniment if you hit the actual note. In other words, if I play Cmaj7 (C-E-G-B) the bass in the accompaniment will play a C. If I add a G below the Cmaj7 it will play a G in the accompaniment. So if you want a slash chord you have to play the chord exactly - Cmaj7/G. Incidentally, I found the DGX fingering to be very restrictive - only multi-fingered mode and only below the split point. Also a very limited set of voices below the split. Couldn't get to grips with it. Maybe you should get a PSR. Even my old PSR220 had more features than the DGX, including all the finger modes.

Bryan