People have been reporting issues on this very thread between the E18 and the S4. It's said that the reason the SIII is less problematic with certain DACs (cf. the E07) than the S4 is because the latter uses 4.3, the former, 4.2.
James of FiiO talked about that in the early development stages of the E18 and there have been several threads on the subject of the S4's compatibility generally -- here, on XDA and elsewhere.
The original Nexus 7 also handles USB audio less problematically than the Nexus 7 (2013). Again, this is thought to be because the original was built around 4.2, but that seems suspect to me, since the whole point of buying a Nexus device is the frequency of rollouts and both models should have had 4.3 (and, lately, Kit-Kat).
Sorry to hear of your issues with the S4's display -- if you find a moment, please PM me about that. The display is one of the best things about my S4 and the biggest reason I chose to buy that model and not the SIII when my original Galaxy S died and I could no longer wait for the S4.