I was looking to get my wife a 02 M750 a while back, and called Power Commander on this same issue. They told me they didn't have one for the M750 and didn't recommend using a different model... I do know Ferracci offers one though.
We did eventually get my wife an 02 620, (which PC doesn't make a unit for either) and ordered a Ferracci unit for it. It was a bit more expensive,(MSRP) but they did gaurentee it to work...and it does. (They will also build you maps depending on what mods you add in the future)