"Wave superposition and cancellation" applies to ALL frequencies - not sure why you read suppression into that
It may be that is not his problem BUT it is very easy and inexpensive to check - he can simply hang some rugs in various places in the room and test
The kef LS50s have a good reputation, but aren’t easy to test.
Take a look at his pic and if anything it seems he has too much reflective surface... yet another reason to get some analytical equipment in there and find out what is really going on
Still need to hear answers to the questions about what he had in the UK...
One more idea: just maybe it is not a room-speaker interaction (less likely, but...) - he can take the speakers outside and test, OR turn them off and borrow some headphones to test
It may be that is not his problem BUT it is very easy and inexpensive to check - he can simply hang some rugs in various places in the room and test
The kef LS50s have a good reputation, but aren’t easy to test.
Take a look at his pic and if anything it seems he has too much reflective surface... yet another reason to get some analytical equipment in there and find out what is really going on
Still need to hear answers to the questions about what he had in the UK...
One more idea: just maybe it is not a room-speaker interaction (less likely, but...) - he can take the speakers outside and test, OR turn them off and borrow some headphones to test