It could very well be something as “ordinary” as your audiophile visitor brings his watch and or cellphone with him into the room. Watches and clocks have the peculiar effect of degrading the sound. As I stated previously somewhere watches and clocks in rooms at big HiFi shows are one very big reason the sound usually sucks. I wrote a paper on it with Peter Belt, it wasn’t that long ago.
Best to have visitors check them in at the door. Experiment: take all watches, clocks and cellphones to another room and listen again. Then bring them back into the room. Ugh, right?
Or it could be that you’ve simply moved from your ideal listening position to give your guest the best position.
The most obvious reasonS for sound sucking at hi-fi shows are:
Very high ambient noise levels
Very high seismic vibration
Less than optimum rooms…size, shape, reverberation time
EMI soup from all the switched mode power supplies and chargers
Very poor network bandwith
Very high network traffic
Overloaded mains supply
Poor quality mains infrastructure
unstable room acoustics as # visitors change
Lack of equipment equilibration time
Lots of new gear insufficiently run in