I just got mine today.
I do not consider myself a die-hard audiophile, I just want to hear my MP3s and FLACs reasonably well, that's why use an LG G6 handset and a set of Beyerdynamic DT 770 pro 80 Ohms.
First off, The Aurvana SE included in the bundle are not very bad. I also tried a pair of Nokia by Monster and the Aurvana is much brighter, although a little weaker. Beyerdynamics do sound better than both.
Now, about the Amp. At first I used it simply as an amp and, compared to the quad DAC of the G6, is much more powerful, G6's amp is not even close. When I turn X-Fi on, the sound is completely different. I'm not sure it's better all the time, some songs benefit from it, some lose. The thing is that it can be very fun sometimes, Hans Zimmer's Live at Prague opening medley sounds just great.
I do not remember very well, but I have the feeling that I could achieve similar results with Viper4Android, back then, when I had a rooted Galaxy Note 4. But phone rooting is getting less and less necessary and for me it's not worth the fuss anymore, so these extra effects are nice to have.
Bottom line, I'm glad I got it. The amp alone is really good and I will definitely need it when I'll buy new phone that won't have a good DAC like LG's. As fot the X-Fi, it surely deserves to be turned on at least once in every song, just to hear how it sounds. I just got a feeling that this little thing really drains my phone's battery.