Out of pure curiosity I decided to see what 2 HomePods in a group with the left HomePods right channel muted and the same for the right in muting the left channel.
Hmm. Works ok but the reason for doing this was to see if I could curb the HomePods boomy bass. One of the reasons I do not use them for music unless I have to. At first I though adjusting the DSP to reduce the sound level of 100hZ and below by 6dB. 6dB being what I believe the lower frequencies are boosted by.
My attempts failed as shortly after making adjustments it appears the HomePods auto calibration to the room kicks in and boosts the low end again. I know this as when I turned of Parametric EQ the bass was extra boomy and then reduced to the normal boomyness.
So, HomePods as Roon endpoints are pretty pointless in my opinion.
Or has anyone found a permanent way to adjust the EQ without auto calibration u doing it.