I typically ask them what they think of the system, and explain that is more important than what I think.
They sometimes ask what I have, and want to listen. I let them listen to my system, and answer questions they may have that deal with my system. But I am careful not to compare it to their's. I let them make comparisons, and if they decide they need to look at upgrades, graciously will offer help.
I see little value in demeaning a persons choices, especially if they are really proud of them. It is also helpful to know a bit about where they are coming from and heading to, audiowise.
