Hot is an old school term for the positive side of a pair of terminals. "... installing 47K resistors at the input jack between the solder cup and the hot for each channel ..." means remove the positive wire from the RCA jack center terminal (solder cup) and install the 47k resistor inline between the wire and the now vacant RCA jack center terminal.
------------wire-------->] RCA jack center terminal
becomes
47k resistor
------------wire----/\/\/\/\---->] RCA jack center terminal
I think there may be a picture of this buried in the gallery somewhere. If I find it I'll attach it here.