Latest RBS750 firmware compatible with NBR750

My NBR750 is running the latest available firmware (4.6.5.11_1.5.66) and my three RBS750 satellites are running firmware version 4.6.5.14.

The latest available firmware for the RBS750 is 7.2.6.31 ... but this is not offered via the admin GUI (which reports that the firmware is up to date).

Is this simply too new to be compatible with the NBR750?  Are there any newer compatible versions?

I'm having trouble with one of my satellites (which needs to be daisy chained via another satellite rather than connecting to the router directly) where it will run fine for a while then lose sync and refuse to reconnect.

I'm wondering whether a new firmware version might help but worried that if I go above 4.6.5.14 that it will no longer be backwards compatible with the router.

Any and all advice gratefully received.