I listen with my Sennheiser HD598 and a USB soundcard (Sounblaster XFi Pro). I am under the impression that the sound quality is decent at the very least. I have read though that the impedance is higher for lower frequencies and as a result of that the lower frequencies could be insufficiently produced by my current soundcard. What DAC and amplifier would be a good solution for me? Is it certain that the sound quality would improve? I guess I would have to connect the DAC by USB. I intend to buy a better headphone in the future (for now a DAC and amp might be a better investment) so that headphone also has to work well with that DAC and amplifier. I am a noob with regard to this, I don't want to spend a lot of money for something that looks more impressive than it is. I just want the sound to be produced as realistically as possible.