Does this audio amplifier do differential filtering?
What you're actually (technically) asking is: Does this amplifier have common mode rejection?

Common mode is the noise/disturbance that is the same on both wires of a differential signal. Read more here.

Assuming the schematic is accurate, then the answer is No, this amplifier does not have common mode rejection, but read on!

Indeed there are circuits that can reject (we circuit designers don't call it filtering) common mode signals. This circuit does not have such common mode rejection.

Fortunately, you will still get the common mode rejection that you want!

How does that work?

The actual cancellation of the commonmode signal will happen at the speaker. 

Suppose there's a common mode disturbance on the input. As it is common mode it will be present on both signal lines (of the XLR connector). As the amplifiers are equal this signal will also be amplified equally and appear equally at both output terminals with the same amplitude and phase etc.

Then at the speaker this signal will also be common mode, so present at both speaker terminals when measured with reference to ground. But the speaker itself is "floating" between both outputs, it has no ground connection so the speaker does not "see" that common mode disturbance! That means the common mode signal is ignored at the speaker.