As I mentioned in this thread earlier, my M-Audio Code 61 also powers up through the USB port of the Ketron SD90 without any issues. The SD90 module acknowledges the connection of Code 61 as a storage.

I was able to play on the Code 61, triggering chord changes on the left hand for styles, and solo voices on the right hand, with no frozen touchscreen. Deane's Roland A-800 could be drawing too much current from the USB port of his SD90 to interfere with the touchscreen operations. A separate AC power adapter should be a good solution.

Thanks,
Paul