Hi Eric,
I’m jealous that you can get those results with the Fritz alone. And fully agree, I also do not believe the access point improves sound (other then maybe radiation onto the equipment). It only helps setting up a clean channel in a space with lots of interference. Actually, now that I know a bit better how it works, I think two 902ac units (one as access point and one as a client) with openwrt and external antennas set on a narrow 5ghz channel could most probably be a great lower cost solution to areas with lots of interference.
Cheers,
Bosko