Well, we need to go from digital to analog to drive loudspeakers, and we need to control gain. Multichannel is no different from stereo in that respect (just > 2 channels). But as we can decode multichannel formats (including Dolby Atmos) on a source device, upstream of said DAC/pre-amp, we don't necessarily need/want an AVR/AVP. Especially as they don't usually measure well (with some exceptions at higher prices).
For a while I relied on source device software to adjust gain (in the context of playback volume) but doing that you are just one software glitch or user error away from a blown speaker so I'd say don't do that. When my existing stereo DAC failed and I decided to give myself the option of multichannel there were roughly two choices—exaSound or Okto—apart from pro audio interfaces (and only one you could actually buy). At least one more choice now, I'd say more is better.
Now I'm happy to have the DAC and pre-amp functions in one box, but separate boxes are also functional. From a Mac source it's straightforward to aggregate a number of stereo DACs for multichannel (Mr Rubinson did and wrote about this at length). Then you want something to control overall gain into the power amp stage.
But that remains a small market niche, so I'll not be expecting same from BoXem out of the gate.
Edit: added use case for analog box.