So here's my subjective review:
Mobile phone used: Asus Zenfone 3
Headphones: Creative Aurvana SE
The supplied headphones are very comfortable. About the most comfortable headphones yet. The earcups are supersoft. My ears didn't feel any pressure or discomfort even after almost an hour of listening. The sound is good but with the SXFI Amp, sound stage expands and the sound seems to come into my ears from outside my head instead of from the headphones. It's hard to describe. But yeah, after listening with SXFI Amp for a while, your ears and brain will get used to it and you will miss it if it's turned off.
Headphones: Tunai Drum
This was a surprise. These are in-ear headphones so it is impossible for them to provide a sound stage but put them in the SXFI Amp, choose Outlier Black as the headphone profile(there isn't a profile for the Drum) and suddenly these earphones come alive. Like literally. Listening to Madeline Bailey's cover of "Radioactive", I was blown away by the accurate and resonant sound of her guitar strumming and her voice just felt so close like she was singing right next to me.
To sum it up, the SXFI Amp is an "experience". You may or may not like it but you gotta try it just to see in which camp you fall in.