Many-to-many (m2m) networking is a communication paradigm for provisioning numerous types of network services. In this paradigm, a group of hosts exchange information between its members in a synchronous way. We focus on two impairment aware dynamic routing approaches for m2m communication: direct full mesh connectivity and replicated transmission using rendezvous servers. Furthermore, in the latter case several client-server assignment (CSA) schemes are proposed. We provision m2m transmissions in Elastic Optical Networks (EONs), being the next step in development of optical communication. The main contribution of the paper is performance comparison of several impairment aware routing schemes using the metrics of m2m session blocking probability and spectrum usage. In our extensive simulations, dynamic server assignment using fallback replica selection always outperformed the static client-replica coupling.