John, one thing that I thought you might have tried with the BK-7m is incorporating it via MIDI with your Yamaha. I agree that the Yamaha has some better RH sounds and a good style selection. But one application I thought would be a no brainer would be to take the Yamaha's drum track, and mute it in the Yamaha, and send it to the Roland...

Best of both worlds!

This business of having 2 or 3 MOTL arrangers, and then combining them into one über-arranger is what makes the idea of having more than one work. If every song is more a case of 'I'll do this on the Korg's arranger section' and 'I'll do this on the Yamaha', even though you may be doing RH voices on all of them, you are missing out on the best that they can do. Each arranger has strong points and weak points. Combining them with MIDI (you'll probably need a fairly decent master keyboard to pull it all off) is what will give you the most variety and quality of sounds.

Imagine a song with the Yamaha's guitar parts, the Roland's drums and bass, and some comping from the Korg. Now imagine that each song you do, you can pick and choose different (but related) styles from each arranger for the parts you want. Your style choices just went exponential, as you get a huge variety of possibilities rather than relying on one arranger for the entire arrangement.

If I ran multiple arrangers, this is what I'd be doing...