In my experience cables really don't do much at all, if anything, to the sound.
Using your E7 as a DAC, you're most likely getting better audio, assuming its DAC is superior to the one in your PC.
That being said, the differences DACs and amps make, in my experience, are not nearly as profound as some would have you believe. A better amp will likely result in tighter/punchier bass (unless you're coloring it with tubes), and a better DAC will likely result in more clarity and separation. These differences are usually pretty subtle, but once you get accustomed to the changes, they can make or break the sound for you.
When I was auditioning DACs with my dad over the weekend (with his B&W 800 Diamond system), there was one particular moment that was truly striking to me. It was when he played a percussion track (Sheffield drum track), which I had heard countless times before. When played on the Weiss 202, through his speakers, it was the first time I ever experienced a truly live feeling. I could picture the drums in front of me perfectly. It was quite the ear opening experience for me. Oddly enough, going to another similarly expensive DAC couldn't reproduce what I felt with that DAC. It was strange, and somewhat saddening. At best, I could say the differences were subtle, but it was the difference in between uncanny valley and reality.