I'm using the E30 in a stack with the L30 HP Amp and both convinced me that probably I won't need to upgrade anytime soon. Both with a Hifiman Sundara and an AKG 240 I get nothing but transparent AS-IS quality.
It sure reveals huge differences in how each music is recorded/mixed/mastered but this is not a problem at all! It just shows how many different approaches find ways to appeal to the listener. Don't waste your money if you are only looking for a more transparent sounding DAC. Only spend more if you are after more features and a better design.