It's just a couple of buffers - the 10k/1k sets the gain at 0.1, shorting the 10k's would make it 1x. The two op-amps with outputs tied together with 1 ohm are

It's just a couple of buffers - the 10k/1k sets the gain at 0.1, shorting the 10k's would make it 1x. The two op-amps with outputs tied together with 1 ohm are just creating a virtual ground (effectively paralled to double the current handling). I can't see how this could reduce 'hiss' if it there's something wrong in the first place,all seems very unlikely though. Possibly it eliminates hum (which mobile devices are generally hideous for, when charging) but the details are likely to be setup-dependent. Or maybe RF is leaking out of the phone causing the hiss in those particular headphones, and all this is doing is stopping that.