The two HST vehicles you make reference to in the later part of your post were market test vehicles 41178 and 45084: These were converted in late 1992/early 1993 to demonstrate and assess various new features that were proposed to go into the next HST refurbishment which would have taken place between 1995 and 2000 under BR had privatisation not intervened.
41178, converted from 42011, was the FO that was fitted with headphone jacks at each seat where passengers could select from four channels of CD music and two radio channels (BBC Radio 4 and Classic FM). Music from a CD could also be played over the PA, but this wasn't often done.
The other vehicle was 45084, which was converted from TGS 44084 into a new Trailer Standard Conductor Disabled (TSCD) vehicle. This was the carriage that featured the new design of guards' office and was created in response to concerns that the guard was too inaccessible right at the very end of the train in the TGS and aimed to relocate the guards' office to the centre of the train, as the TSCD would be marshalled next to the buffet car when in service.
The two carriages featured a lot of prospective features that have since become standard in modern train designs and others that still haven't found widespread use: Electronic seat reservation displays, electronic passenger information displays above the saloon doors and a disabled accessible toilet.
They were unveiled at Derby on April 19th 1993, and then went into service from May in the formation of the "Master Cutler" HST working to and from St. Pancras on the MML. They transferred to Laira in mid-August for use by Crosscountry, where they were regularly employed on the "Cornishman" working from Penzance to Edinburgh/Aberdeen. They were then later reallocated to the Great Western where they were used on the "Golden Hind", but with the advent of privatisation they fell into disuse (No more hope of a BR refurbishment to test the market for) and have subsequently both been converted into TSOs, 42360 and 42362 working for FGW.
I've heard about the Intercity XC Voyager service retrospectively, but I'm too young to remember Crosscountry operations before the early days of Virgin (And even then never had any dealings with first class). It sounds like the sort of thing I'd like to see make a come back in order to make my long Crosscountry journeys a bit more pleasant.