Ok so the answer to the GLM subwoofer question is that GLM can only integrate Genelec subs. They are very expensive for what they are.I have an "old" Tact 2.2X digital DAC preamp that has XLR and RCA outputs and digital outputs as well... And it has a physical volume knob... which I also prefer over software volume adjustment...
I was going to suggest a Trinnov to integrate other company subs. Can your Tact do this task?
Also i’m not sure you would need a sub for an office situation.