If this is for stereo listening, you'd ideally want stereo subs, at the current price of all this gear, I'd sell the 5200's and use the money you'd get for those plus what you'd have spent on the subwoofers on some nice 6Ks. You'll get a huge upgrade across the board and the bass will be plentiful and well integrated.

HC: 861v4/ID40/LPS, DSP5000, DSP5000VC, DSP3100, SW1600, HD621, Oppo BDP-105, Sony VPL-HW55ES
2-Channel: Oppo BDP-105, TEAC VRDS-7/Trichord Clock 3/PSU, 551, Quad 303, Harbeth Compact 7ES-3, Kimber cables, Russ Andrews mains and supports.
Previous Meridian: 5000C, 5200SL, 7200.2, 6000, 562V.2, 568.2mm, 800v4, 808.2i, 818v2/v3, 861v8, 502