Haven't been following the thread closely --- what will the headamp be based around?
IIRC, the iCAN and iDAC were TPA6120 and MAX97220 based, respectively. Since these are all modern IC based headphone amplifiers (well, for the iCAN, the TPA6120A2 was supposedly used just as a current buffer, utilized some kind of inductive trick to avoid the use of 10 ohm resistors for current stability), would iFi be willing to consider trying out new parts, such as the ES9601? On top of being very, very high performance in terms of specifications (122 dB SNR, -117 dB THD+N), it seems to be designed for mobile use, and draws power from single 3.3V rails (stepped up via an integrated charge pump) and eliminates DC blocking caps, so it'd be suitable for being powered by an USB power supply. On top of that, the 20-QFN package is really, really small, allowing space for other components. Other details are sparse on this yet-to-be-released part, but I assume it has good PSRR and all that jazz as well.
Edited by tomscy2000 - 4/8/14 at 2:20am