Hi Ty,
What I have is the handheld AVX mic + receiver and a lapel mic/TX + RX.
As you may know, this equipment has very limited display info and I don’t know how to get the firmware (even if one can get it displayed!)
serial nos
handheld mic body: 1265101294
lapel mic TX unit: 1445107246
RX unit: 1185102056
RX unit: 1445108859
When Sennheiser returned the units, there was no paperwork to indicate Firmware either.
One of my sets was older than the other and that created pairing issues. They fixed it completely and for free (which surprised me) but then they admitted that since firmware upgrades can only be done in-house then units had to be sent back on a no charge basis.
I was quite impressed by their customer commitment!