By dissing chamber music in that way, GP was falling prey to an unfortunate Hollywood stereotype that usually involves rich people and this piece of music:

https://www.youtube.com/watch?v=OSV8NnA3B74

But what about this one, also by Mozart, also performed by the Hagen Quartet?

https://www.youtube.com/watch?v=ZBMpD5ldrWU

So Mozart had a lot of emotional range, even in a period where sharp dissonances and tangled counterpoint were out of fashion.

A group of us chamber musicians has had a lot of success playing for people that don't usually listen to classical music simply by doing it in intimate bars and cafes. (Primarily, the Revolution Cafe in the Mission District of San Francisco.)

The fact that the music is long doesn't matter at all if you find people where they are and play with emotional conviction.

It's a loose collective called Classical Revolution, plays 1st & 3rd & 5th Mondays, been going since 2006. I'm only there occasionally these days; I might show up August 19. Starts at "8:30", often actually later, goes till 11:30.

The evening typically starts with a group that actually rehearsed and then devolves rapidly into the closest thing you can have to a jam session when you're playing notes off a page. Whoever shows up decides what to play on the fly from our collective piles of sheet music. It's a risky format—some nights are great, some less so. :)