Good, this is a result... you have to set static ip for the 2 ps3, because now it works but it would not work in the future. For the lags and join issues... i dont know, maybe the slower down speed (6.5) could cause the lags... i think that 2 ps3 joined to the same match from the same LAN could cause some conflicts!
I have a ps3 and i set the dmz.