not to hijack, but i'm in same boat as this dude. Was looking at just getting a Dragonfly and an external HDD that is bus powered and connect to my Macbook Pro via Firewire or Thunderbolt. I would then play music off of the ext HDD and output via USB>Dragonfly>NAD integrated amp. I was going to use some of that heavy duty velcro and stick it to top of laptop and slap the HDD on to it.
I have a relatively decent audio set up now for CD/SACD playback in my main listening room (QSilver Line stage pre, Kingrex T20, Sound Dynamics/MMGs, (depending on mood), Tjoeb '99 (probably could use an upgrade), and DacMagic (1st gen) but wonder if this digital set up would sound decent enough. Is there a issue with playing off external as opposed to using internal HDD on the MBPro?