We just walked a house that has the original speakers and wiring from 1990. There is one pair of wires (16/4) at the home run that feeds 6 different pairs through the house. There are VCs at each speaker pair location in each room. We didn't have time to take the speakers out but we looked at one of the VCs and it wasn't a 70V VC. We looked for some type of hidden autoformer that everything might wire to or Bose gold amp from back in the day and we couldn't find anything. However, the way the house is laid out made it so we couldn't track all of the whole house wiring (no crawl space in many of these areas).

Any ideas as to what might be going on wire-wise or a best practice to track things down?

Thanks in advance