Thanks for the explanation. Just to clarify, I am a science graduate (although not in electronics) and have worked in the automotive industry (ran Honda's Technical Training Schools for some years) and more recently in IT (database development). So yes, you could say I'm a technical kinda guy and Ohms Law etc is not exactly unfamiliar. However, the principles of electronic design are beyond my experience, hence my need for explanation.

My requirements will be for the outputs of the BMW radio module to be fed into an AudioControl 6XS which will handle active crossover duties and pass the signal onto the Nakamichi amps which have an input sensitivity of 0.2 - 0.8V, but it seems to me that it's the 6XS that needs to be able to cope with BMW's balanced signals, yes?

In any case, I have determined that Genesis' (the UK amp people) Hi Level converter is happy to accept the BMW 5V balanced signal and will output a single ended signal suitable for the input of any amp. Problem solved

Thank you all for your input.