No, you don't need a switch.
One Unicable II LNB on 19E. Another Unicable II LNB on 28E. Both connected to single cable. When you install you "tell" the LNB that is aligned on 19E to only respond to requests for 19E. Same for 28E. At the other end you split as required to distribute to all your receivers.
Now any STB can access any Unicable LNB over the single cable.