I'd def ask to dem both, and bear in mind that the DSW will likely integrate more easily and use SpeakerLink, as others have mentioned. Remember the 861v8 has MRC (Meridian Room Correction) built in, and you may find this, in combination with the DSW works very well indeed.

Also, you might consider trying the system without a sub in the first instance and see how you get on - in my experience the 5200s were far from being short of bass by themselves! You can always add a sub later on if you really feel you're lacking in the low frequencies, and you might save some money in the first instance.

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