The X6M uses the S63B440O, the M5/M6 use the S63B44T0. There are quite a lot of differences, compression ratio is higher for the latter and the DME is different.
Interestingly the US supplied S63TU engine manual (
http://f10.m5post.com/forums/attachm...8&d=1360771557, page 3, full load diagram) quotes the output of the S63TU as 560hp/412kW.