You cannot use a splitter with the dual tuner. You need a separator. To make it easy for you to install the superdish, you can use DP44+ switch instead of
dp34. You can get one line from the switch to the dual tuner, split the cable with a separator and use a diplexer to connect to the other TV. The bad part is that superdish comes with dp34 switch not dp44+.
(splitter devides the same signal into 2. Separator separates a high from a low signal)
BTW: You also can not use separator to feed 2 receivers.