I use a setup similar to yours ( Mac OSX ) and I own both the Dragonfly Black and Red. I bought the Black first but after using it for a while I decided to buy the Red ( and eventually sell my Dragonfly Black ). Both sound great for their price, the Red does sound noticeably better though. The problem I had with the Dragonblack was the anolog volume control, with my my Hifiman HE-400S (32 ohm) I'm only able to use the first 4 bars of volume in Mac OSX, without using alt-shift it would be impossible to find the right sound volume for me, anything above four bars is too loud, honestly it's barely usable. The Red has a digital volume control with much more evenly spaced steps. With harder to drive headphones like the Sennheiser HD600 (300 ohm) it's less of a problem to find the right volume with the Black, but the Black doesn't seem powerful enough to drive the Sennheiser, it's sound thin and unbalanced compared to the Red, both are loud enough with the HD600, but sound vastly different. The Black has a maximum output of 1.2 compared to 2.1 volts for the Red. Again with headphones that are much easier to drive like the HE-400S the difference is less noticeable. Also because the Red has an output of 2.1 volts it can be used as a DAC connected to a line in on an amp, the Black will work as well but the 1.2 Volts is below the spec most amps are designed for and could cause sound quality problems.
Black + easy to drive headphones = good sound, terrible volume control
Black + hard to drive headphones = poor sound, OK volume control
Red + easy to drive headphones = great sound, good volume control
Red + hard to drive headphones = great sound, great volume control
Don't make the mistake I made, buy the Red right away. The differences on the spec sheets seem small ( analog vs. digital volume control, 1.2 volts vs 2.1 volts, better DAC chip ) but they add up.