The LNB you need depends on what satellites you hope to pull in. Most FTA KU sats use linear polarity so you need a linear - either standard or universal. DTH birds (like
DTV and DN) use circular. Either way you need a DiSEqC type switch for use with FTA receivers. DN SW's will not work; generally, any LNB that has a built in switch will be incompatible with FTA switching. Some people have reported success with the DN DishPro switches but I think this is not verified as 100 % compatible.
Furthermore, the toroidal dish uses reverse-polarity LNBs and these are sometimes hard to find.
kat