I have a battery powerd Nico sound labs head phone amp that i use with full size CD player, the twin batteries last for ages, goes loud and is very very well reviewed in say places like rockgrotto.........if you get back on the head amp idea, i'd be interested to see if you could make one as good as his stuff at the same price or better........i've had his main supply amp stuff too, very nice, but i got my portable converted to take RCA plugs and well it sounds a lot better some some stuff i've heard...........