How about external DAC?

From computers, Android, even iPod you can use external DAC. Soundcard which usually have PCI express 2.0 interface is also a DAC too.

For computer, it's just a DAC connected with USB cable. For Android, use USB OTG cable, then connect the OTG cable with USB cable to the DAC. iPod usually have a 30-pin connector to male USB cable to connect to a DAC. But not all DAC have USB port. Some DAC only have optical and coaxial input, so a USB to coax/optical converter is made. The reason why using optical/coax is to remove jitters. As on the picture below, jitter is a point of frequency where it peaks. Of course peak at high frequency is disturbing. Jitter is caused by the powerline of USB. That's why audio grade USB cables are made, also stuffs like USB isolator.