Audio switch - Low pass filter

[zathrasb5]

Hello,

I am working on an audio switch.  In summary, it will be spliced into an existing car radio on the FM line between the radio and the amplifier.

So far, I have, starting with the FM line, a high pass filter (16 hz), a voltage bias to Bring the line up to 4V, the Switch (Max 4053), and another High pass filter (to pull the 4V back out).  The signal then goes on its merry way back into the amp.

A though occurred to me. I may need a low pass filter between my input signal, and my output signal, to bias the signal back to whatever the radio has it biased at. 
1)  For this low pass filter, assuming I construct it with an RC, what is to stop the low pass filter from wiping out my signal on my output line?  2)  Do I need a resistor on either side of the capacitor (R19). 
3)  If so, is this the full resistor value for the filter, or 1/2 of the value that I otherwise calculate?
4)  Am I making my life more complicated than it need be?