SDR is not eliminated in V9, but DASH is certainly the preferred method for replicating magnetic libraries. The impact from replication should be reduced, and DASH does allow for similar throttling rules depending on the links. The overview section of the DASH goes over the other advantages it has over the SDR.
Based on your post it sounds like you want to go from Site A to Site B and also Site B to Site A. Is there a reason for such redundancy? Is Silo or tape based aux copy also in the mix somewhere?