Just a simple output on/off switch is all you need for the line output. Unplug the headphones when not in use. Best of both worlds and no unnecessary relays or switched HP sockets.
Might be the Halo. I happen to already own a balanced switch box and spare cables for the line outputs so I can mute the speakers when using headphones. Midgard integrates well with my (AKM chip version) Modius. Running on low gain, with low distortion. And running USA-made, USA-serviced gear. But I still have to get balanced headphone cables to test Halo.I usually have my head amp within arms reach.
I would guess it has something to do with the whole Halo deal.