I opened up the E30 DAC, very nice build quality, DAC as listed above OPA 1612 opamp which seems to be well liked by some and not so much by others, so far I like it just fine but will know more when I hook up the tube amp. Funny how I like to setup low cost but great audio and just not into the very high end gear when I used to have multiple race cars I built up to $100k into some of them.
I spent a ton more on car audio than I ever did on home audio because I seldom had time to listen to it, usually out doing sports or building race cars. I did have a sound quality competition Tacoma, first big system Mac amps, Dynaudio drivers, Zapco processors, DAC, etc...beat a prior world champ in front of his NFL starting linemen customers:) Then rebuilt again, $25k in gear(retail, I paid about half) $7k component speakers with 100 watts per tweeter and 200 per midrange, custom built Arc Audio amps, custom built dual midbasses with 300 watts per driver. Custom built subs with 1kw each. Custom modded Image Dynamic crossovers,
dual 20 bit ladder DAC, 20V balanced out of DAC and through processors, had some serious dynamic range.