Hello,
i now had the Creative SXFi Amp and the THX Onyx here over the weekend.
Both get plenty loud with inefficient lower impedance Cans like modded T50RPs.
The Creative has a little bit more power with high impedance Cans, i wish the Onyx had this too, it is borderline (No Headroom).
Sadly in comparison the Creative SXFi Dongle sound a little compressed (in the matter of space).
On several recordings with multiple layers of sound and instrumentation it sounded agitated, listening is rather stressful.
The separation is not as wide and clean as the THX Onyx, on less complex recordings it is not that striking though.
No i did no scientific blind testing, but my basic setting for this devices was fairly unbiased.
I even let my wife listen to both dongles, to get a second opinion, so to say "non-partisan"
She couldn't find the terminology, but she said the SXFI sounded uneasy in comparison and she couldn't grasp some of the background instruments as clearly.
The XFi Spacial Sound is unusable for music, a nice gimmick for Films, but i dislike the strong reverb.
Build is good and i really like the physical buttons, this would have been a bargain at 60€.
I had a strange problem with TRRS Headphones, some times the SXFi would not play until unplugging and replugging the headphone.
For now the Onyx may stays...