Interesting observations. What was your setup before using the AudioQuest Dragonfly?
I use a Fiio E7 with my MacBook right now since I'm not ready to shell out $200+ for a DAC/amp yet. I'm not too Shure if I would be able to detect the differences should I use the custom cable.
I was using a Fiio E17, which I previously (and still!) love. I think the dragonfly is a step up from the Fiio, but to be fair, I should go back and repeat my experiment using the Fiio E17 with lossless material only. I DID try ~190 or ~256 kpbs through the Dragonfly and found it extremely difficult to discern a consistent difference between the 2 cables. From my experience, if you're not using lossless, or near-loss material, the other variables won't make as much of a difference.
Just to clarify .... I went back to the E17 and played only CDs (lossless) .... and once again had a very difficult time distinguishing between stock and custom cables. With the dragonfly .... no problem. So you WILL need a decent source (not sure if your E7 will cut it). At least to these ears. YMMV