nimoSGI believe it's a modified PCM69 or some flavor of it. they don't give specifics because they do a lot of modification with the standard chip so that it fits their goal of producing the kind of sound they like. it's not sabre (thank goodness) and is a warmer, more musical sound than you find in most of the delta sigma stuff you find today. they use this same chip in their micro iDSD, the new retro, and will replace sabre in the updated iDAC. here is a discussion of it from their lead tech designer on the choice of DAC: http://www.head-fi.org/t/711217/idsd-micro-crowd-designed-v0-16-beta-firmware-calling-iclub-members-page-135/60
gyamsno one knows the exact model cos' ifi refuses to disclose... but people think they know cos' they dig the web and ifi keeps them guessing... seriously?