@nyev On the basis of the points you made regarding the powering of the Phoenix's I decided to overhaul the setup of the powering of my digital sources.
Cable-wise, I previously had a couple of old Ecosse Big Reds, an unshielded Russ Andrews Yellow, and an entry level Isotek Multiway mains block - all of which were very 20th century.
The first change I made was to purchase the current Isotek Evo3 Gemini to feed both my Innuos Zenith Mk3 and Phoenix USB, and this made a huge improvement in pretty much all areas of sound quality. I was very pleasantly surprised, as I assumed the various high-end linear power supplies in the Innuos boxes wouldn't be that sensitive to power quality. I expect that reducing RFI/EMI as much as possible is the goal here.
Emboldened by this, I ditched the Russ Andrews for Belden 83803 to feed the Isotek, and re-terminated the Ecosse Big Reds all with MS HD Power Blue plugs (silver), and transferred my existing QSA light-blue fuses across. These feed the Innuos boxes from the Isotek. All cables are now fully shielded and earthed.
The improvement across the board is quite something. I can't say for sure if spending big money on better power cable makes a difference to digital sources, though it does seem to me that filtering and shielding with the aim to reduce noise into the Innuos boxes should be enough to get you most of the way there.
A few months ago, I consulted with the UK QSA importer, having heard significant gains using QSA fuses with my Hegel H390. Interestingly, he spoke more enthusiastically of the gains from also using QSA wall plates. Of course, I have to take his "advice" with a pinch of salt - though my curiosity was very much piqued. It's probably a itch I'll have to scratch in the future.