Well, I stated in my HD review that the Berkeley Alpha was quite a nice improvement, but questioned the diminishing returns vs the $250 Matrix X-SPDIF. It is clearly better, but...
On the EX something has changed, and I am coming to the conclusion that either the USB section is cleaned up, or the fact that I'm now running the USB connection powerless (my newly added JCAT USB card allows for powered 5V or unpowered, and I'm running it unpowered to the Chord EX)....one of those aspects seems to be the reason that the difference between USB and SPDIF (and then the differences between SPDIF converters) is much less evident with the EX. Also, I don;t have the Berkeley here right now, but I don't sense that my Matrix X-SPDIF (nor the Audiobyte Hydra X+) is essential to the setup like it was with the HD. I'm still trying to figure this out.
As stated above, I added the Audiobyte Hydra-X+ to the mix, but have had a hard time hearing any prowess over the Matrix X-SPDIF. Additionally, I uncovered a firmware bug that Audiobyte is working out currently....DSD channels are reversed via the Hydra-X+. Thsi is somewhat fixable with JRIver (swap the cables and then tell JRIver to swap the PCM channels....and since DSP doesn't work with DSD all is well).
The jury is still out on all this, so far. But currently I am not losing sleep over playing via USB (rather than SPDIF).