FreeAXP/AvantiFlex NIC Emulation Question

I have several FreeAXP emulations, and 1 AvantiFlex emulation running in a heavy load network environment. Does the emulator use hardware to filter network traffic for packet meant for the particular NIC, or is the NIC an all software implementation?

I ask because the AvantiFlex emulation does not seem to get any better performance for network operations than the FreeAXP clone emulations I run side by side with the AvantiFlex system.

The NIC is an all software implementation. The same soft NIC is used for FreeAXP, AvantiFlex, and Avanti.