This is perhaps a very late reply from someone who has only just, today 25 November 2007, signed up to this forum having been in the field since 1972 in terms of equipment and reading about it in the British Wireless World magazine now defunct, since the late 1960's!
My reason for writing is that I wanted to correct one issue, that of the availability of Matrix H hardware during the time in 1977-8 that the BBC were playing with it. In fact Sansui's line of QRX receivers were all equipped with Matrix H and later Matrix HJ decoding via variomatrix, by the intervention of the tape monitor, which was modified by Sansui Audio Europe SA, in Antwerp, Belgium, for the United Kingdom market as distributed here by Vernitron of Southampton, Hampshire, United Kingdom.
The QRX7001/777 and later 999 also carried this modification along with the QSD-2 in the U.K. by the same means and for the same purpose. However just to make it complicated one of the U.K. dealers obtained non official imported units and marketed these without the addition of the piggy backed circuit board as found in the genuine units.
It was therefore (at a premium) the QRX9001 retailed at around £700 in 1977 with high taxation, (try double the figure of $1400 US), heavy 240 volt mains cables and much uprated over the U.S. and especially U.S. Post Exchange Models, the many of which were reported as seconds from the production line in Japan, that it was possible to hear the BBC,4 Channel radio broadcasts in this country.
We were served by a dedicated Sansui showroom in London's Maple Street, next to the Post Office Tower, which even offered at a premium, to upgrade non Matrix H units after sale, to update QR to QRX decoding with variomatrix and which was heavily at the time, advising the cinema projectionists in London, on how to get the QS encoded tracks on Hollywood 70mm film, out into the auditorium, via modified QSE encoders, with built in decoders for the benefit of what Masaya Ishikawa (Sansui Showroom Manager) described as the "People with long hair, sloopy Joe pullovers, jeans and Jesus sandles."
Of course this was all a very long time ago, but the much uprated QRX9001's continue to give stirling service having not missed a beat in all the years since they were made. I have two of them, one purchased new in 1977 and the other from Chandos Studios in Colchester England, the contractor who made possible the RCA Records series "Classic Film Scores" mostly transcribed into CD-4 Quadradisc. Chandos who went on the produce QS encoded vinyl and later CD issues, turned eventually to Ambisonics, but at the time wanted to be able to demonstate to their customers, the amazing CD-4 records, recorded in England, that they had had involvement in producing at the Kingsway Hall and other London venues.
Four Tannoy Lancaster's worked with the QRX9001 for this purpose and having sold them the receiver was left unused for years in its box. I bought it a couple of years ago via U.K. E. Bay, with no complaints.
Hope that this adds to the knowledge of Quad fans everywhere. Best wishes to all who come by this late edition.