Using Selector to Mux and Demx in a single graph

[Luke Berndt]

I think I maybe trying to do something that is impossible. Can you have a graph 
 where it goes:
- a Source
- a Selector with one input and two outputs
   - Block 1 processing
   - Block 2 processing
- a Selector with two inputs and one output
- a Sink

I want to be able to dynamically switch between 2 different demodulators in the 
middle of a graph. Ideally I would be able to the combine streams from either 
active branch and only have a single sink. Is there a different approach that 
would work? Steam-Mux will not because it blocks waiting for input to 
interleave. 

If I have separate Sinks for Block 1 and Block 2 things work fine. If I use a 
second Selector to chose between Block 1 and Block 2’s output, no messages go 
through the graph to the Sink.

- Luke