For the record,
REF1000 was what BCD released first. It was fundamentally just a B&O ASP1000 module inside a BCD box.
REF1000 Mk II was added later (also available as an upgrade for REF1000 owners). It added an input buffer and a power supply board for the ASP1000. IMHO this was a big improvement in sound quality.
Then BCD released the REF500S and REF500M (stereo and mono blocks respectively) with the third generation ICE modules. I agree the newer modules have a sweeter sound vs the older second gen ASP module in the REF1000/MkII.
The REF500M included the same input buffer and power supply board as the REF1000 MkII.
I guess at this point there was some confusion. Some customers might have been expected a REF 500 Mk II when the 500M was already enhanced the same as the REF1000 MkII.
So there was a decision to rebadge the REF1000 MkII as REF1000M to keep the branding in line with the REF500M.
There is a new BCD mono block power amp based on NuForce modules though. It is UBER expensive.