I'm using the Matrix Audio SPDIF 2. I bought mine from Arthur Power, a great guy and a very reputable/helpful dealer of Matrix Audio, Violectric, other non-US brands.
- FWIW, I got an immediate sonic bump just by switching out my old SPDIF converter (not a DDC) to the Matrix DDC. Same coax cable, but better sound w/the Matrix. I thought the sound "tighted up" somehow, is more focused & integrated. A subtle but meaningful sonic upgrade, whether heard from headphones or speakers/sub
The latest version, the SPDIF 3, costs more than my $399. Here's the "3" on Arthur Power's website:
https://power-holdings-inc.com/Matrix-X-SPDIF-3-Femto-Clock-&-Format-Converter-p470184380
You can still get the "2" version for $399. Here it is on Moon Audio:
https://www.moon-audio.com/matrix-audio-x-spdif-2.html
What's the difference between the "2" and "3" versions? Apparently it mostly concerns the IIS (html) output to the DAC:
"Compared with the previous generation, the IIS-LVDS output isolation is added, which completely isolates the digital output from the ground wire of the USB end, and bids farewell to the annoying noise of the USB front end. In addition, it supports up to 32Bit/768kHz PCM signal and 1Bit/DSD512 signal output, achieving an excellent output quality from both PC and mobile devices."
So if your DAC has a IIS/html input and you know you'll be using it, spring for the "3" version.
But there are many DDCs out there. And the ones said to be good usually cost 50%-100% more than the Matrix. Caveat Emptor.