With PS Audio’s BHK Preamp, I have the balanced outputs going to the amps and the rca outputs going to the subs. When I connect my older Conrad Johnson tube pre and tube poweramps in the system, I use only rca connectors (no balanced xlr connections) and use rca y-splitters after the preamp. I would check with Schiit if their preamp can output both balanced and rca at the same time.
The other way to connect a sub, is thru the speaker outputs from the amplifier, but only certain subs allow for this type of connection.