Was doing a spot check on an audiobook through one of the audio interfaces the other day, then transferred the file to my Macbook Air and listened to it there as it was transferring to the iPhone. The quality difference was startling, with the MBP not sounding nearly as clear and transparent. Since then I’ve been listening through my portable iRig Pro Duo while researching portable headphone amplifiers. Looks like the Apogee Groove may be the best option when working with a computer but I’ve found nothing outside of the Apogee One and the iRig Pro that works with the computer, phone, and iPad. The One and iRig both have the same problem though, they’re small but still a little on the large side for an everyday, toss this into the bag, headphone amp. For now the iRig is working great and I plan to do more testing on the Mac and interface sound differences.