Supex SDT 1000, excellent condition, a couple of small marks only. A superb step up but I've bought a posh Audio Note SUT to match my Io, so this may as well go.
Sounds great with the Io and matches with most vintage cartridges, such as Supex 900, 1000, 1100, 2200, Koetsu, Kiseki, Dynavector Karat, Ortofon etc.
As with all SUTs some care must be taken over placement to avoid him. This unit was completely silent in my system when used with shielded cables and sited on a different shelf to active (powered) components.
Some spec from the web.
Ideal impedance of the cartridge - 1.5 - 10ohms
Resistance - 47K ohms
Step-up ratio - 1 : 100(40dB)
£250 Inc UK delivery
Supex SDT 1000, excellent condition, a couple of tiny mStep-up ration*: 1 : 100(40dB)
Indeed, my guess is we aren't meant to know and if I were actually interested in this I'd take the advice of the people above and drop Bryston/PMC an email to confirm authenticity.
It's another one of life's/hi-fi's mysteries.
The 859 is 13W and the 869 is 15w, had both and the 869se is very much the better amp. Not sure it's what you are looking for with the Tannoy's though. If you are near me you can borrow my 869se to see.