I could be wrong, but from my experience with the tailgater, you can't have a regular splitter in between a 211k and the tailgater. The signal has to be able to go back and forth. You need a switch with 2 inputs, 1 output, and the data can flow both uphill and downhill.
I would check radio shack and explain to them you need a coax switch with data being able to go up and down hill.
I can't tell if this one allows signal to go uphill or not.