Audio Friends Don't Let Audio Friends ...

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.

This is not about truth or lies this is about your opinion and it would not be inappropriate to state that it sounds different to your ears. We bought a tube integrated amp and a knowledgeable audiophile suggested that we upgrade the tubes, so after spending $500 on upgraded tubes we were disappointed in the new sound. We called the tube store and they said it would take 80-100 hours for the tubes to break in and now that they are seasoned the change was more then worth the wait. . Maybe the new components just need  break-in time. FWIW!