Next piece of equipment decision

I'm the proud owner of a Pulse 2i and am enjoying it very much. Now trying to decide how to make it even better.

Decision: Add a second Pulse 2i or a Pulse Sub +.

If I go with Pulse 2i, does it only run with partial output in L/R mode? Or would I place in opposite side of room and run both in Stereo mode?

Room is ~450 sq ft and has lowish ceiling and a hardwood floor.

Had to mothball old school HiFi due to WAF and looking to replicate best I can.

Appreciate feedback or other ideas.