The best way to balance out that setup would be a nice pair of 7200s grin

I'm sort of half joking, but also not. The 7200HC is a beast, and a lovely speaker. I would think you'd have to dial that back so much to 'match' the M6s, firstly it's a bit of a waste of a 7200HC and secondly, I'm not sure you'll ever quite tonally match or blend them in whatever you do. Be interested to see if you are able to achieve a satisfactory blend there.

HC: 861v4/ID40/LPS, DSP5000, DSP5000VC, DSP3100, SW1600, HD621, Oppo BDP-105, Sony VPL-HW55ES
2-Channel: TEAC VRDS-7/Trichord Clock 3/PSU, Avondale S100, Harbeth Compact 7ES-3
Previous Meridian: 5000C, 5200, 7200.2, 6000, 562V.2, 568.2mm, 800v4, 808.2i, 818v2/v3, 861v8, 551, 502