I always assumed that M-6 and M-1000 responded identically to Sysex, but it seems they are not that compatible - the Matrix-6 is not responding to remote editing commands for the Modulation Matrix. So it seems that the Sysex command for editing a MM path seems to be exclusive to the Matrix-1000 - I had a look at what I could find on the Matrix-6 because I couldn't believe it, and the command sequence is not there. 

Can anybody confirm this: no remote editing of the Mod Matrix on the Matrix-6 - apart from sending a whole patch, that is