Audio Friends Don't Let Audio Friends ...

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.

You didn't say if they asked for my opinion.

I have experienced this. Although nowadays I wouldn't say any change is "major". Most equipment is good. They asked. I told the truth with the caveat that some people prefer different things. But if they hadn't asked I'd let them enjoy whatever they thought.

Be honest! if he asks your opinion, tell him how you feel. Remember, it’s just a feeling you have. Nothing else!

I tell them there stuff sounds bad if that's the case.HELLO!!

Jsmith-

If you are invited to listen to someone's system and finish the 1st song

I feel like the host is waiting for some sort of an expression

of your impressions. Maybe they aren't but I always am. 

So regardless of whether they ask  or not the dilemma still exists.

In the end your suggestion is to follow Bambi's mother's proclamation 

that "If you can't say anything nice, don't say anything at all". 

Still makes for an awkward moment for me.