Has anyone here heard of/familiar with the Bryston 4B pre-amp? Can't seem to find much info on it on the web, Bryston's site doesn't seem to have it either so this must be quite an old model? It is a line level pre-amp with no power amp section and must have preceded the current 4B ST/SST power amp models. Approximately how old is it? Can it still be upgraded or do Bryston not offer such a facility? Is there much that goes wrong with it? Any information on this is very much appreciated. Thanks!