need a better sound source?

Thanks to all of your advice i bought a mega turntable; and Sennheiser HD7 xx with the cavalli tube hybrid. I've only listened to the phones with my NAD system and nearly cried (literally) when I heard new levels of clarity on a James Taylor record that I never heard before (i've lost significant learning in the upper range - hence the emotional response) So my question relates to listening music out of the computer. I use iTunes and everything is downloaded from cd at the highest quality and have a dragonfly plugged into a usb port, which will then be plugged into the cavalli. I assume that listening trough a MAC with a Dragonfly is not going to give me theist sound out of my phones. Do i need need sound source ? Expensive cables from house to the cavalli? or is there a portable device? Because of the times we are in i don't have huge amounts of money to lay out. But since my hearing is so challenged I want o get a good a hearing experience as possible. Thanks in advance. I am a professional musician. 

The Dragonfly is ok — I use a Dragonfly Red, but with your amp and ‘phones you will be rewarded by investing in a better DAC.  If you give us your budget and share what sonic properties are most important to you I’m sure you’ll get some excellent recommendations here. 
so the dac is the weak link, not itunes.
in that my budget is a couple of hundred and I do like a warmth to the sound thanks. Really love to hear the clarity of vocals
The Cobalt Dragonfly is a bit better than the Red......but its the old bug-a-boo. How good and therefore expensive do you want to get. All earphones do better with a better dedicated headphone amp.  I wouldn't guess that the headphone out on the NAD is that good.  Most headphone out's are afterthoughts in the design...usually an op amp.
I think you might be pretty happy with the Dragonfly into the Cavalli, which sounds like you haven’t heard yet unless I’m reading this wrong?
I am using the dragonfly - i was wondering if using iTunes was the best way to go or am i losing any sound quality by using iTunes? thanks
I’m not sure, but I’d think there might be better sounding options than iTunes.  But if your Dragonfly is lighting up green at least you know you’re getting full CD sampling rates.  Sorry I can’t be more help with your specific question.  I started streaming from Qobuz a year ago and haven’t touched or listened to a CD (ripped or otherwise) since. 
Expensive "audiophile-grade" cables that cost thousands of dollars are marketing hogwash. Cable manufacturers will tinker with the cables’ nominal impedance; in doing so the sound signature will change. Poof! Now you know.

If we actually required such over-engineered cables, manufacturers of audio gear would include them with as to not limit the performance of their products.

You don’t need to spend tons of money on USB cables for audio. The digital signal doesn’t know whether or not it’s been fed through a cheap cable or an expensive one. Ideas about "lowest possible inductance, capacitance, or impedance" are simply nonsense.

Want a perfect USB cable? So long as the power and data lines are properly segregated in the construction of the cable. That’s it!

All you need is....

TRIPP LITE Usb 2.0 Hi-Speed a/B Cable With Ferrite Chokes (M/M) 3-Ft.

These two products together will ensure a clean signal.

And for your source, the Furutech ADL Stratos is a superb value. I trust it for most of my preliminary mastering edits; and it delivers. FYI as a pro muscian, it also has a recording you might find it extra useful.