A very nice portable DAC Amp is the Oppo HA-2SE. These can be had for about $200 on the grey market sites like eBay. Cool thing is the Oppo can also be used as an external battery to charge another device. I love products that serve more than one purpose when I'm forced to travel. It's also an excellent desktop solution I used for quite awhile. Only reason it got replaced was I got into high impedence headphones like Beyerdynamic, Audeze and ZMF.