I have had one of these (Teralink X2) to play with for a few weeks and it should be fully burned in by now.
It is a loan unit so no tinkering with insides, it has the external PSU and has been running from that.
There is an ASIO driver and control panel available for download for this unit and I have been using that.
The unit will default to 48KHz output SR and needs to be manually set to 16/44 via its control panel to avoid upsampling.
(which may have led to some of the negative feedback from users)
I am not much interested in hi res as I have mainly CD rips.
As an S/PDIF converter I found it fairly equivalent to an M-audio firewire 24/96 into the same 2 DACs (nothing of the Killer class) - a modded Beresford Caiman and a DIYParadise Monica2 much modded.
Neither were to the standard of my Marantz CDP as a transport through the same 2 DACs, though not terribly below.
It was better than the Beresford USB input (uses PCM2902) eg USB -> X2 -> S/PDIF -> Caiman was better than USB -> Caiman.
Changing the input board on the Monica to use i2s was a noticeable improvement over the S/PDIF from the same unit.
To the point where it was almost comparable or possibly equivalent to CDP transport with S/PDIF.
I listened to a lot of music through this over 3 or 4 weeks and while it is not "special" it is not awful and I have not felt badly deprived, though I am in need of a vinyl fix now
My system, my music, my ears - YMMV
It does provide buffering of the i2s signal which allows reasonable length leads to be used, and making up a patch cord from a Cat 5/6 cable not hard to do - the wiring can be checked from the wiring diagram printed on the case using a frequency capable DMM.
John Kenny is now offering a modded Hiface with i2s output but much more $$$, likely sounds better too.
Added a day later:
thought I had finished playing with this, but today had a brainstorm and plugged the PSU into my Black Box instead of the generic board it was plugged into and fitted a USB isolator device and NOW it IS rather good indeed through the i2s/Monica combination. Think it might be time I did some serious re-organisation of my power leads and supplies and look at some DIY filters. This is the third time recently I have had a similar experience of marked improvement through getting power leads away from SMPS jiggers which I rather suspect are putting grunge back into the mains.
Maybe I need a submarine battery