It affect both, its a DC blocking caps
What mod could I do to use this same card with AKG K601 headphones? In another thread about modding PCI x-fi cards the OP recommended LM4562 opamp. Can I use this one with the x-fi surround USB too?. Also is it feasible to unsolder the DAC and changing it by another better one one? It seems difficult as the DAC has quite more pins that the opamps.
No you cant change DAC as it pinout are different even though the number of pins are the same. I have modded mine and one caution, don't use LM4562. LT1364 is a better opamp