can you please illustrate how you are using the 1K resistors?
Ideally, it should be like R output ->1K Resistor -> Mono input<-1k Resistor<-L Output
two resistors should be connected together at one end and connected to the input of the Mono Amp and the other ends to the outputs. If you want to be totally safe,Use a couple of 470uF capacitors in series to decouple, and a 47K across the mono amp input