Regarding the sounds of the Midjay Plus, do you know these demos?
http://www.ketron.com/sounds.asp?mod=MIDJAY Plus
http://www.ketron.com/sounds.asp?mod=SD2The second link is for the SD2, but the sounds of SD 2 and Midjay Plus are absolutely identical (statement from Ketron).
I own a BK-7m, all in all its sounds are really good, some are great. Strings and acoustic guitars are rather average. IMO, from what I hear in the demos,in some cases Ketron has an (slight) edge over the BK-7m (maybe some trumpets, saxophones, large strings, acoustic guitar, maybe also drums), but for other instruments it might be vice versa, and the BK-7m has a wider choice of sounds. Given the price difference, the BK-7m seems to have a much better value for money.