Ok, but my SW21 switch didn't work well because they are too far from my IRD.
I bought a DP34 to connect 2 IRDs or more, and only with 2 cables inside the house. (instead of 4 with 2 sw21)
So if I understand, I need to plug 4 cables on my 2 lnb, connect with 2 sw21 that connect to my dp34...