I've got a folder full of firmware from the "suite" of software that was distributed for a time by Meridian. It included all the install, command, update and legacy software including a folder full of firmware for all models up to that date. There is a folder for the v4 and the DSP7000 but nothing for the 5200.

I don't have the speakers and went from an 861 v1 to a v8 so don't know anything about whether latest firmware versions are are present for your models but if you know the file names I can look or send the folder if you want it.