Hi Guys....
Here is the final word on the subject...Unless Mackie (or the company doing the bios upgrade chips for Mackie) has a back stock of the "SST 29 EE020 120-4C-PH" proms, there will be no more bios upgrades. I have done an exhaustive search looking for them, and other than a place in the U.K. that wants an outrageous price for them, and a company in China that wants a 200 minimum piece order (and has a bad reputation for taking money and not sending the product), there are no more to be had. Neither Digikey, Mouser, nor Future electronics, has any, and they also have no idea of where to get any. I couldn't even find them on "EvilBay"....so, I'm sorry to say, if you have them, you are the lucky ones, if not, sorry to say, you "S.O.L."
On the MDR to HDR side of it... I should have another batch of those eproms tomorrow, but this was about the last of those eproms too, so, get them while you can if you have an MDR that you want to upgrade to an HDR.
SteveT