Why won't iTunes stream 320 kbps audio across a network?
Do you know for sure it is the 320 kbps that is keeping the songs from being played? Can you play songs with a lower bitrate successfully? 

There are three reasons I can think of that would make a song not play in Shared Library: 


You have reached the 5-computer limit
on Shared Library. Only when the
number of concurrent connections gets
back to less than 5 you will be able
to connect and play the songs.
The remote iTunes has not been
authorized for that Apple ID and the
song you are trying to play has DRM
protection (i.e., it is an Audible
book or it was purchased way back
when Apple only sold DRM-protected
songs).
The song is listed on the Shared
Library (and on the "server" iTunes
Library) but it is pointing to a file
that does not exist on the computer's
file system or is out of reach.


I hope this gives you additional ideas to look into.