There are other considerations than the voltage drop, that you need to be considering. Specifically, offset voltages (and drift),input noise ( both current and voltage), and parasitic input capacitances. As you go to the large resistors, the stray capacitances start forming low pass (generally) filters that will start rolling off your highs, and affecting the high frequency phase relationships. If your inputs are not matched (including symmetric layout), these parasitics will be different for each channel, further degrading your sound.
Also, the type of resistor you use can make a difference in the noise floor of the amplifier. Use good quality metal film on your input, I would not be surprised at all to be able to hear ( and measure) a noticeable difference in the amp, by changing the type of input resistor that you use, especially if you are using 470k.