Streaming server behind loadbalancer buffering errors

We are running 4 windows 2003 Standard servers behind a
Alteon 180 Fiber Loadbalancer,

Windows 2000 Worked fine and we could connect till 800Mbit
per machine.

Now if we get more connections then 300per machine The
players start buffering.

Are there any new issues concerning TCP or Healthchecks we
need to take notice of in our loadbalancers.

It looks like the windows machines are not broadcasting
anymore to the loadbalancers also