TIme to progress from back to front story. To reshuffle the deck accordingly, the Lio DHT was benched in favour of the D1 DAC/pre from COS Engineering. Though a fully balanced deck, it would run both Pass and S.A.Lab single-ended to use the same cable into the latter's direct-mode input. This signal path was pure solid-state.
Pass Labs XA30.8 vs. White Knight. The core difference here was about a pervasive softness associated with focus and grip. The Russian played it more polite and gentle/genteel. This was a full-bandwidth effect but perhaps most dominant in the bass where the American exerted more apparent woofer control for more profundity and foundation anchoring. Whilst not affecting subjective soundstage perspective, the White Knight sounded more distant and farfield because of its minor vagueness. The XA30.8 sounded more powerful with the usual things this entails: more propulsion, drive and forward communicativeness; more firmness, substance and slam when called for. This offset still enlarges when COS D1 and Pass connect via XLR (which merely is an observation about how they interact, not about either sounding better in RCA or XLR mode).