I'll guess this will go against the grain but an observation I've made with headphone amps for my 300R and very easy to drive Sennheiser HD580's is that the amp matters very little. Just a couple of Volts at a few mA is enough to drive 'em and I can tell very little difference between various SS sound sources driving them from CD player, to DAC, to headphone socket on PC or laptop or even my own design no compromise class A headphone amp.... yes the latter is the best but to be honest the difference between any of these sources is Nth degree... I wonder if this is maybe why some "designed to be coloured" headphone amps, mainly valve, have become popular?
Often there are resistors in line at the output of headphone amps or the sockets on an integrated amp, 22-68R or so being common, which means they have bugger all "grip", "current", "control" over the 'phones by design even! My class A no compromise unit eschews these but with little difference to the sound...
Arkless Electronics-Engineered to be better. Tel. 01670 530674 (after 1pm)
Modded Thorens TD150, Audio Technica AT-1005 MkII, Technics EPC-300MC, Arkless Hybrid MC phono stage, Arkless passive pre, Arkless 50WPC Class A SS power amp, (or) Arkless modded Leak Stereo 20, Modded Kef Reference 105/3's
ReVox PR99, Studer B62, Ferrograph Series 7, Tandberg TCD440, Hitachi FT-5500MkI, also FT-5500MkII
Digital: Yamaha CDR-HD1500 (Digital Swiss army knife-CD recorder, player, hard drive, DAC and ADC in one), PC files via 24/96 sound card and SPDIF, modded Philips CD850, modded Philips CD104, modded DPA Little Bit DAC. Sennheiser HD580 cans with Arkless Headphone amp.
Cables- free interconnects that come with CD players, mains leads from B&Q, dead kettles etc, extension leads from Tesco