Each replication job is independent of the other, so yes, it is multiple streams.
A dedicated 10GBE link between two DSS servers is so affordable nowadays, I can finally start recommending it. A CX4 10GB adapter will probably cost a wee bit more than say a 4 Port Copper Nic. Many Supermicro mobos have 10GBE built onto the platform. It's better for overall cable management, IRQ management and performance.