in wall wiring

Class A was maybe the wrong word (it was early morning here when I replied) ;)

What I ment was a buffer circuit (either Solid State or IC) like the Burr-Brown BUF634 with two times gain. Put a 50 to 75R in series with the output and 50 to 75R to Gnd at the receiver end.
The two times gain will then be one again, and your choice of cable is almost free..... You could use normal standard shielded cable or coax (with the same impedance 50 or 75R).
This way you will have a much higher current flowing in your cables, and the cables will not be so sensitive to radiated noise and less sensitive to cable quality ;)