Sort of. The base voltage in the absence of any interference will be exactly half of the input voltage for any reasonable resistance value there.

"Interference" adds and subtracts small amounts of current, resulting in higher or lower voltages on the I2S lines (or possibly the other way around, but with the same end effects). If the normal current flow from the two resistors is significantly higher than the "interference" current flow, then the interference won't have much effect on the results.

Making the resistors smaller in value increases the current flowing through them (thus more heat), making the signal stronger relative to the "interference" sources. Or at least that's how I see it.

EDIT: But if you go too small on the resistors, too much current may flow, which could damage the empeg which is supplying that current. 2K/2K puts 4K-ohms between the (5V) input and GND. So.. Ohm's Law says 5V/4000ohms = 1.25milliamps, which is safe enough. 1K/1K would draw double that amount, which is then beginning to approach the high current side of things.

Cheers
-ml