well i recently sold my hd580's after years of disapointment. I found them dull and 2 dimensional even with a musical fidelity headphone amp. yes they could go loud without distortion but that was about it, they made all my music lifeless. So i thought i'll just buy some cheap headphones and use the amp socket.............at 1st the koss portapro sounded good for the £20 i paid..........but seemed to be a bit rough at higher volumes................so as i am a great believer in 'burn in / break in' i discoverved that 4-5 days later of constant play at moderate levels (not too loud) has paid real dividends..............yes the drivers are smaller than the hd 580 but they are interesting, fun, detailed, bass is great, sometimes a little too revealing ! which for a £20 head phone is quite something. i would say they are like a semi quality sports car compared to a boring saloon (hd 580).............just wondering now if they justify getting another headphone amp again.........don't want to spend out on gadgets that are gonna make no real difference like last time ..............seems to me a lot of head amps are just fancy boxes...........would any portapro owners like to recoment a head phone amp that they found to be good with these phones..........