How do you power EU items? and how to ship an item to USA?

I submitted questions on their official website, but no replies.

May I suggest you just order one? I use two, somewhat more upmarket, and the effect is excellent! The wall-warts supplied work anywhere in the world

I know some people use step down transformers.

Only thing you might need is a different plug or adapter. The provided AC/DC converter looks like it would work workd wide. It only needs 7.5 volts. Look through the photos of it on the site you provided it shows the plug. 

talkskiwon, there are two types of USB transmission to DAC - synchronous and asynchronous. The first one relies on computer to create timing while asynchronous USB sends data in packets and DAC recreates timing with its own clock. Most of the newer USB DACs use asynchronous scheme since computers cannot create reliable jitter free timing. Chances are that you have newer asynchronous USB and this device won't do anything - just wasted money (check it). Using good USB cable with data lines only (no power) might help. Device that filters out high frequency from the data line might help, but this device offers reclocking with "ultra precise clock" that most likely you don't need.  What is your DAC?