Need a piano bar/cabaret-type spot for about 20 frustrated singers to have a blast on a Sunday Afternoon?

I have been given the task of organizing an event for a group of about 20 singers to have a get-together in Manhattan. Most of us are native New Yorkers, but many in the group don't do much in midtown or downtown. So it's up to me to find a spot where we can do sing-alongs AND eat.

We are not trying to break the bank so I know that I may have to settle for eating first and then rolling on over to a piano bar, and that's fine.

I am pretty savvy about the city but my brain is just not clicking on this one. So yes, I am aware of the Duplex, but it is too small. Brandy's is small and not in an interesting neighborhood (though there's an Irish pub with good burgers nearby).

Not interested in chi chi places like the Algonquin. And I want the possibility of musical interaction (open mic / singing along) so a spot like the Monkey Bar is out.

So I am turning to you all to help me out here.

THANKS