Need help with 828es silent “From Computer” outputs

[tremo]

I’m setting up a new Dolby Atmos 7.1.4 speaker system (with IK MTM monitors), and everything’s (mostly) working fine. In the early testing phase; no DAW involved, just playing Atmos from Apple Music. Using 828 Analog Outs 1-4 for L-R-C-LFE, and feeding a Behringer ADA8200 from Optical Out A for the 8 surround channels. Mac Studio to 828es via Thunderbolt. 828 Routing screenshot attached.

In the Mac Audio/MIDI Setup, I’ve reduced the output level for all those channels to -14dB to keep things at a sane level. However, while that’s fine for my Audeze headphones, it’s too low for my Sennheiser HD600s. So I want to move Phones 2 to a different set of outputs -- say, From Computer 19-20 -- where I can independently raise the level.

I can’t for the life of me figure out how to get audio to pass through any “From Computer” outputs other than the ones I’ve already assigned. The Phones outs look right in Mac Audio Devices (see second screenshot).

Help! I'm stumped!