Right, the e10k is not what I wanted at all. My own fault for misinterpreting the photos.
What I have: a DAC and amp that only accept one source - a micro USB input.
No analog routing through the amplifier available. (well, ok, you can put a line level in into the line out jack and listen to it through the headphone jack and even attenuate what you hear using the rotary volume control. But it's going physically through the case rather than logically crossing an amp path.)
What I thought I was going to have was a choice of a USB DAC or an analog in and an amplified analog out, relying on USB to power the amp.
Suggestions on what I might want to look into? I would like to feed it from a larger variety of analog sources than digital ones, to be honest. I have a USB OTG cable and was able to get it to run off of my phone's usb port but that feels kludgy as all get out, and it didn't get anything like as loud as I was hoping it would. My list of how often I'd use the inputs would be in this order: mini stereo, analog RCA jacks, USB. There's spdif and digital coax out on a few things in the house, but the connectors have not been used in more than a year, so really it's those three sources I'm interested in.
At maximum volume I want my ears to rupture. I can dial the volume back on my own. If the volume is only about as loud as one of my tablets could drive it to begin with, it's not what I'm looking for, particularly since the headset I intend to use this with is less efficient than the ones here at the house - I picked up a set of the Sennheisers on black friday and the tablet (tab pro 8.4 running cm12) can make them edge of loud, but the phone (nex 5) is just hopeless and the computer at work is marginal. At 100% gain from it they're a little too loud, not "oh, god, turn that down" loud.
I will take the box to the office tomorrow to give it a whirl connected to the laptop, but I had expected to be able to use this with my phone's headset out, which sounds OK so long as you keep the output gain low. Obviously with relatively insensitive headphones, no actual pleasure is derived from listening within the non-clipped range of the phone's output stage.