Netmap. Example to understand?

[Jog Lie]

Hello

I have three boxes running linux or freebsd.

A is a loadbalancer to b and c. Same network.
A has three nics: one for internet, one connected with B and one connected with C to avoid another switch for a small configuration.

I wish to understand how netmap can help me saturating a 10Gbit link with a i7 3930k (could be replaced by something less powerful if netmap allow big perf jump).

How can i select the nic to which i wish to send the packet? The read write pattern is not clear to me. Will netfilter be completely bypassed hence achieving high perf?
I am in need for an example mates.
 Thanks a lot
Bye