I know this is an old thread but I was just wondering how you got on?
I have had various pairings of bunnies - firstly two females, who tolerated each other but would sometimes fight and had to be watched (we ended up splitting them) a male female pair who got on well but the female was overly dominant and tried to steal food and hump my boy bun constantly (the girl was much younger and smaller, he is a big bruiser but a big softie!)
When my girl rabbit died my boy was really lonely and we had no choice but to get another bunny. We picked a slightly older bunny (7months) as my other rabbit is now 4 and a bit, so an older boy. We put them in together and they bonded within an hour, and are totally inseperable and the best of friends. The ironic thing? They are both boys!
It is very much down to the personality of the bunnies, more so than gender in my opinion, both of my boys are big sooks who love their food, and who have really foot temperaments, generally boy rabbits are more friendly than girls so if yours is a boy and is neutered, I wouldn't rule out another male - ill post pics of them together later and you can see what I mean!