The MOTU Ultralite Mk5 is a nice piece of hardware and is even at a great price point if you use more than a tiny fraction of its capabilities, but it also costs quite a few times the entire cost of the rest of this system :)
If you just want to get the eARC data, any S/PDIF input (USB or I2S-via-hat) would work just as well at 1/20 of the price :)
I want someone to fudge up a multiple shairplay setup (presumably by claiming multiple IP addresses, as AirPlay 2.0 apparently can’t handle multiple sinks at the same address) that can use a single multichannel interface like the Ultralite Mk5. This would make an excellent multizone audio setup at an entirely reasonable price.
Personally I use an eARC extractor to run S/PDIF to an audio interface (MOTU Ultralite Mk5) and an RPi running camilladsp handles room correction and active crossovers. Overkill at the moment for just a few studio monitors and a sub, but it'll be a great solution when I get around to building some custom speakers.