If you have V6.10, the last firmware version you can use on your processor board is V6.14, which was released some time in late 1997. The upgrade is by means of PROMs.
In order to install V7.12 and newer firmware, you would have to get a new processor board. That's the upgrade kit you mentioned. These newer boards were used in late production 8720D, 8720E and ES. The same board was also used in the 8753 series. These newer boards do not use UV proms. Updates are done via floppy drive (another thing to consider when thinking of USB floppy emulators - they may or may not work for that).
While they fixed some bugs and added some features in later firmware, they also made it worse in other areas. There is at least one serious bug which was introduced and never fixed. I can't remember which revision that was, but it may have been after yours.
Using John Miles' utilities, you can do all the useful things that the later firmware revisions implemented. One new feature of the later models was ecal, but on the 8753/8720 series the implementation was clumsy, with a glue box. I have no desire to use it.
Does your D have any options installed?
Vladan
