I would say, "That's a really interesting system. Tell me about it!" That steers the discussion to how he acquired the equipment, what he likes about it, etc. People love to talk about their gear. If he comes over to your house and *asks* to hear your system, let him hear it. He might be just as "polite," or he might say, "Gee, I like this better," in which case he might ask you to help improve him own system.
Try to admire what he's accomplished or purchased. OTOH, if he starts saying "Come on over and we'll do some listening!" then at some point you're going to have to be honest and say that *your* system suits *your* ears better.
I had a dear friend who passed away a while ago. He had a fabulous record collection, but I never thought his system was all that great. But I enjoyed having beer/wine with him and talking about this and that, so I let the music spin, made positive comments about the record and the musicians, and left it at that. OTOH, one of the best musical evenings I ever had was with a lovely gentleman who had a terrific 78 rpm jazz collection and an old KLH Model 12 system with speakers stuck here and there. Didn't matter a bit, the music was fantastic.