David, doing my best to figure out your system from the post, I take it you're injecting a cable signal to the feed from the LNB with a multiplexer, then splitting it back out at the cabinet to the sat receiver and a cable box? If this is correct, you probably only need a multiswitch to split the LNB feed, after the diplexor. If your system is configured differently, before the diplexor, then please post more info. There's no such thing as too much info, and in order to figure certain parts of the system out, sometimes we need info about the whole thing. If this turns out to be the case, a multiswitch (which is very different than a splitter), for 2 outputs is rather inexpensive.