In your setup Server A will consume the most bandwidth due to the icecast server, taking into account you have more people listening with the player.
Server B will not consume any bandwidth of those connected directly to Server A's icecast server.
Now if you have most of your listeners or viewers using the web front end on Server B then Server B will use almost the same bandwidth as Server A.
* Server B should not use more bandwidth than Server A, unless all traffic to and from Server A is from the web front end. In this case Server B will use more bandwidth but it will be marginally more. This extra bandwidth will be from making connections and loading the front end to the listener.
Because the bandwidth required for each audio stream will always be the same, the only difference would be how its presented to the listeners. The web front end would have some extra overhead that the IceCast server wouldn't have. So doing a strict comparison of "listening" bandwidth between the 2 servers would show Server B using slightly more bandwidth.