Hi Christian,
You can have one Wowza instance ingest the incoming streams and transcode these into different qualities, and have the edge/load balancing client servers serving your client connections. The edge servers would not need to do any transcoding, but would just need to pull the streams from the origin. This was covered pretty succinctly in this response from rrlanham.
You would then just need to configure your current server as a load balancing master, and configure additional servers as the load balancing clients. Your streamers would not need to know about the edge servers, and your client connections can be properly redirected to the least loaded server.
Here are some tutorials that may help you:
Scaling and Load Balancing Overview
Michelle