I agree with your other responses, I think this is not valid but I'm not certain. I'd like to find out from an expert just to be certain.Some consider me to be an expert... the idea that a tube preamp can do anything to a solid state amp in particular is a myth plain and simple. Coupling caps being old has nothing to do with it. Its just a myth and no matter who is trying to propagate it, its still a myth.
Solid state preamps have coupling caps too and are just as failure prone in this regard as a tube preamp.
Well the fact is that all sorts of things can cause amp-dangerous thumps! This is not a solid state/tubes thing, because solid state preamps can easily make thumps! This is why many solid state preamps often have output muting protection relays. Many tube preamps do as well. But a protection relay is just about guaranteed to mess with the sound, so many preamp designers expect the operator to have some common sense and follow the procedure below:
Its just a matter of being careful- when turning on the stereo, always turn on the preamp first and wait for it to stabilize. Then turn on the amp.
But my friend is a Dr., so I have to respect his professional even though I still regard it should be safe or little risk only.Apparently this is an example of having a doctorate but still having no clue about what one is talking about. In this case his opinion is just that and its bunk.