Here's a ridiculously inexpensive upgrade that will make greatly improve the sound of headphones and desktop speakers. HiFiMan's Express HM-101 portable USB DAC is smaller than an old-school cigarette lighter. But it delivers big benefits to your digital music files. \"I wasn't expecting much from the Hifiman Express HM-101, it's just a $39 outboard USB digital-to-analog converter and headphone amplifier,\" reports Steve Guttenberg in his October 30, 2011 review for CNET.com. \"Well, this tiny USB-powered (it doesn't need batteries or an AC power supply) device definitely pumped up the sound of my Audio Technica ATH-M50 headphones! They sounded significantly better with the Express than they did plugged directly into my Mac Mini's headphone jack.\" At the heart of its DAC, the HM-101 uses a Texas Instrument PCM2702 16-bit, 48 kHz chipset. It also has a line-out jack, allowing you to connect a pair of powered desktop speakers. That's a lot of capability for such a small and inexpensive product!