He mentioned this yesterday and I had no idea what it was until I googled it.
If you didn't know what it was, then logically you don't need it.
Let me bring some literature to the table:
Personally, I wouldn't buy neither the headphones nor the external dac, because it would be illogical to spend a ridiculous of money if you don't even have the proper audio compressions. Because if you have the improper audio conversions, it doesn't matter if you buy a 1 million USD headphone/dac, it will sound horrible.
Is your music lossness or FLAC?
If you buy your music on iTunes, forget it. If you buy physical CD's and compress your own music to a minimum, just like an audiophile would do, then go ahead.
But with music compressed to a minimum, not even the maximum Apple SSD does justice, so your music would be stored on a external HDD just like an audiophile would do.
Honestly, you do not sound like an audiophile and have no idea what you are buying or in the looks of buying. My suggestion would be to research more about the topic, there is so much literature out there in the internet and take a decision based on what you want, and not on what your friend told you.
In order to be an audiophile, you need to have very good hearing, otherwise, you wouldn't notice the compression of the music, therefore you wouldn't mind.
By the way, those headphones, are not what an audiophile would buy, those are only a luxury signature headphones; what an audiophile would buy, are ultrasone headphones, those are truly german engineered, with real proprietary technology, and a set of PRO's would suffice for any audiophile.
Ultrazone
Hoping that my own and personal opinion helps you out.