Keep pushing the estate seller. Since they’ve admitted they sold the head units to someone else, they are ultimately the best source of information. I would imagine, at some point, the person who bought the heads will likely go back to them and ask why they don’t work, or where the rest of the speaker is.

Even if they’ve blown the drive units, it will be much cheaper to repair than to try and source whole replacement heads.

It would be a great shame to break a pair of these. Not just for your own financial loss, but because they are rare and special (and sound absolutely amazing).

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