Friend can't hear me, but he's the only one

Alright here's a weird one. I'm trying to play on Xbox Live via a party with my friend and everything was fine when suddenly my audio cuts out. I can hear him perfectly fine, but he can't hear me. However, other friends I've played with can hear me, and
he can hear his other friends, so it's a specific problem between me and him. It isn't just for the game we were playing at the time, but any game we've played since then. At this point we've tried everything, up to and including:

• Muting and unmuting
  
• Unfriending and re-friending
• Restarting the Xbox (hard restart)
  
• Unplugging and plugging in speaker set
• Getting a different speaker set
• Restarting the router
• Checking connection
• Checking privacy settings

We've tried these fixes on both ends. Any other suggestions about what could possibly be wrong or fixes to try would be awesome. Thanks in advance.

:)