I know the firmware requirement for a Waters Alliance 2695 for Empower 3 is version 2.04. I am not sure why though. This firmware dates back to December 2006. I was able to download the upgrade firmware flash program about 2 years ago off the Waters site. I do not know of its availability on their site now. The zip files must be opened and then placed onto a old floppy disk to be inserted into the 2695 before powering it up. If you can get a good floppy disk and if the floppy drive on the LC is still functional it is quite easy to perform. I have however personally found it a pain to get a good floppy as well as the dusty old floppy drives to work
The only other thing that comes to mind is that a Waters engineer told me I could convert my older 2695's to an E2695. The E2695 has an Ethernet port on board. This lets you do away with using the IEEE bus Lace cards which are no-longer being manufactured. This upgrade requires replacing the main board inside the system. I know that a direct replacement of the older non-E style board cost around 6K. I imagine to upgrade to the new board would cost more. The E series also has a newer firmware version number.
I do not have any Waters 2790/95's so I do not know if there is a different firmware or upgrade for them.