Outlets and Wire Gauge? - Please help!

I finally contracted an electrician to run two dedicated lines - a week from today! I have been reading thread after thread and the consensus appears to be going with 10awg wire for the 20amp run. My problem is two-fold:

1. I'm stuck selecting an outlet because the electrician says that no 20amp outlet can take 10awg, that "10awg is for 30amp outlets".
2. I'm stuck selecting an outlet because of what it might do to my sound. 

I simply want to install something good that's going to feed a Puritan Audio PSM156. I am now running ADG Gran Vivace monos. I prefer a rich midrange.

Additionally, I asked for both a 15 and 20 amp run. People suggested I do this so my sources can be run off the 15A with amps / subs off of the 20A, but someone here mentioned ground loops? I am not well-versed in things electrical. Ideally I would like to know if I should stick with the two runs, and what would be a few good choices for each outlet if I do. @jea48 @erik_squires ... I have seen solid advice from you on the topic of outlets, but they lack things specific to awg and outlet type.

Thank you in advance!

PS I estimate the length of the run to be approximately 50', max.