I think Bernie is saying that he wants to use two USB midi controllers (with no MIDI 5 pin Din out) at the same time with the SD40. One of the USB controllers is his DM48 a midi harmonica.

AJ's solution to use a MIDI merge box is not a viable option for a few reasons. First, Bernie will have to have two Kenton USB MIDI hosts or a USB MIDI host that supports multiple USB MIDI controllers or a USB hub like the UHMR USB Host MIDI Router by Servilla Soft, which I use. Second, even if you feed both USB controllers, after "conversion," into MIDI In 2 (Keyboard), the MIDI harmonica will merely play the same patch as the controller #1. Not much benefit at all. I would be happy to be wrong about this but the SD40 in this mode doesn't allow the 2nd MIDI controller to call up its own sound patch. In other words, both MIDI controllers merged together will play the same sound. However, if the 1st USB midi controller is connected via USB, and the 2nd controller the harmonica to MIDI din 1, the harmonica will be totally independent from the controller 1 and be able to select its own patch for a nice solo melody. This is what I and Curt suggested earlier.

Chris