Bonjour won't work with any security on the wifi. Without security it's fine but is obviously a terrible idea.

Have tried various settings on IGPM but I'm not sure how it should be set up and it doesn't seem to work with any setting.

HELP!

which firmware? Is it on 3.7.3 RC4 or is it on 3.7.1?

The IGMP settings won't really affect (except negatively) any multicast issues between wireless to wired, that's all firmware level and it really should be able to pass all that through regardless of security.

I don't have a 2860 but I use bonjour / airplay through a 2830n, its wireless and an airport express & xbmc setup quite reliably.

It's on 3.7.1 - not brave enough to experiment with the release candidate in a live environment just yet so have plugged in an alternative wifi box for now.