Positive experience with head phone amp
Today i got myself a head phone amp, i had some problems getting good sound out of my head phones on the s4. Compared with the house mixer at the club (djm 800) the sound was really a big difference.
So i got myself Insigna Headphone Amp. I tell you guys straight away the sound was like night and day on the S4. much better! 
Could not find a english site… But i guess there is other companies making these devices. The good thing it was really cheap to
Just home from a 4 1/2 hour gig with no monitors in a big night club.