AMR DP-777, what am I missing ?

essrand, what did you end up using for your cable from source to DAC?

My experience has been (with less expensive DACs than you are using) there is a clear difference in the sound of different USB cables. But also that low cost is not a guarantee of weak sonic performance - some $10-$12 cables sound much better than some $4 or $14 cables - and you won't know what you are getting until you try a few.  Perhaps the generic cable you are using is by luck actually quite good and rivals the pricier AQ job. The greatest success I have had in the bargain rack is with Belkin or HP branded cables with gold plated connectors.

For my reference cable I am currently using a 1.5m solid silver USB cable from Pangea that both I and my hugely skeptical friend have determined sounds better in our systems than what is readily available from the computer shop rack.  I think it is about $80 online at AudioAdvisor. My friend who is an engineer was so annoyed that the cable provided a noticeable sonic difference in AB listening tests that he assumed his generic cable was "broken" and attempted to come up with an empirical test to show himself why the Pangea sounded better.  I think he failed to show any difference in frequency response except with one of the cheap cables tested, even though both the bass and high end sounded significantly clearer with the Pangea. He bought one of the Pangea cables anyway and is listening to better sounding music in spite of his closely held prejudice that it should not. YMMV.