I cannot answer your question directly. But this may assist you as a frame of reference. I have a second system which includes an ARC 100.2 mated with an ARC LS-17 with Dynaudio Focus 140 speakers, Lessloss power cords and Analysis Plus Solo Oval Crystal speaker cable and interconnects. For me, with my taste, it sounds wonderful. This combo is liquid and tonally accurate, with a slight warmth. Treble is sweet and detailed. I believe the ARC 100.2 is one of the most underrated solid state amplifiers out there. Not many reviews, but it does everything very well.
In my main system I use an ARC Ref 3 mated with Lamm 1.2 Ref monoblocks. By comparison, for its cost, the ARC 100.2 offers a fantastic value. Unfortunately, I have never auditioned the ARC LS-12, so I cannot comment. However, I recommend that you audition an ARC LS-17. Excellent tube preamp.
Good luck in your quest.