If they're truly is a friend and asks your opinion regarding a specific aspect of the sound I see no problem with providing a truthful answer within the parameters of taste but only if they ask.
Your friend knows how it sounds much better than you do and unless you live together and if that's the case keep your mouth shut and simply find different aspects to enjoy.
If it's a competition of their stereo vs your's and you want to trash talk and he / she / they are into that go for it but realize that you have opened the reciprocal door and be man / woman / non binary enough to take it for what it is... Trash Talk.
I kinda miss all the robot references.