Far too many unknowns here to justfiy issuing "advice" on the system.
The friend may have a strong emotional attachment to the gear and would be hurt/devastated with negative comments. "Hey, those are XYX speakers. They sound great as long as you don't try to play music through them. And, that (crusty) old receiver. Not worth the postage that it took to send it over here from Japan."
One of my favorite church reader boards states: "A good friend stabs you in the front." So, with that "wisdom" in mind, you can just come straight at them with the "truth" related to all things negative about their system -- including the build quality and esthetics.
But seriously, your friend may have arrived a good point in their system in their estimation. They may have moved past their interest (obsession?) with stereo and now spend their time (and money) in ways that are far more rewarding to them, and their families. Snapping their attention back on the flaws and shortcomings of their system may be unwelcome (at the very least) could make you look like an inconsiderate ---t, an honor that may be well-deserved.
"Wow! I've never heard a system like this before!" Or, "truly remarkable" may be appropriate responses. Best approach would be to listen to see if they indicate some issues with their system and ask for suggestions. Otherwise, leave it alone and move on to the next opportunty(s) to bond with your friend.