Firstly I validated that the hum does still happen when I connect my Kurzweil SP4 into the Bose, so the problem is not the Korg keyboard. Then I found that it does NOT happen connecting into the 2 RCA connectors on 2 other PA systems. I called Bose, and they went through in detail with me and so we concluded there must be a fault with the Bose, so I am in the process of doing a return/ exchange with Sweetwater.

The loss of mic issue may be a different problem. That does happen connecting the stereo TRS connector from the adapter into both the Bose and the Mackie PA. It does not happen connecting L&R separately into the Roland BA330, so I suspect the adapter here. Maybe I need just a TS plug rather than a TRS, but the Bose does state it takes both. Anyway, I'll go to Radio Shack tomorrow and see if I can't get another adapter.

Nobody said life was going to be easy!