I can't believe it: MM7 is running just fine from my old Millennium disk--correct speed, and all. I've created a party and played a few minutes.
I'll give your tips on MM6 a try. As I recall, the Millennium disk set cleared up some bugs that were in the original release. It would be nice to play it outside of Steam! (I went screaming and kicking into Steam, but just had to have it for The Elder Scrolls, which I fell in love with after being shut out of Might & Magic for so long. I also had to have Civilization 6, which I don't like at all--but Civ 5 has a lot of add-ons in Steam that make that game worthwhile.)