I currently own the Shunyata Alpha USB between my Innuos Zen mkIII and Chord Qutest. I use all Shunyata Venom NR power cords, however I use Purist Audio speaker cables and interconnects and absolutely love what they do for my system. The Shunyata Alpha USB has been a wonderful cable as well, but after some recent new additions of Purist Audio interconnects making a huge impression on me, it makes me wonder what the Purist Audio Diamond 30th Anv USB would sound like against the Alpha. Anybody had the opportunity to compare the two?
You didn’t ask about the Sigma USB, but I just wanted to mention that it’s a big step up from the Alpha. Same price as the Purist cable you mentioned. I do like your thinking though about using the same brand throughout. It’s been my impression that this can achieve better results than mixing brands - depending on the brand. Your best bet would be to audition the Purist yourself if you can to see if there is a greater synergy with your other Purist cables. The one thing that I really like about sticking to a single brand is that the benefits stack up predictably as you move up to better models.
On the other hand I should mention that Shunyata has really been on a roll lately with both their v2 power cords and digital cables. The Sigma USB will blow your mind.
(And yes I have not been able to stick to a single brand throughout as my amp requires MIT speaker cables, but they haven‘t seemed to get in the way of me appreciate the Shunyata positives)