Good to hear its starting to work 
The Channel variable is a channel number, but because there is nothing in this verison to indicate which channel is channel 1 then it will indicate channel 1 as the first channel it happens to detect. But the three channels should have different values if you are sending different values on your transmitter.
edit: I just reread what I wrote above and its not correct. The multiplexer will select the correct channel if its gated correctly.
Could you post the sketch that includes the multiplexer code.