My Modwright has proprietary branded caps like Audio Note, from who I dunno. The X upgrade in the PH9.0 in fact removes caps in the signal path. I think it's not just about the caps but where they are in the signal path.
At this price point I would trust the makers to know what works and what doesn't.
Would I have gone into my Tavish Adagio and the Modwright to upgrade caps? Hell no! I know of at least one maker who didn't believe more expensive caps made any significant difference. As long as they were polypropylenes they were good to go.
While my experiments with caps have yielded some good results (EAR834 clone) I would rather depend on the circuit rather than the type of caps that are in there, especially a phono stage.
A fast look shows that Luxman used MCaps in the EQ500, but the basic caps, not any SGOs. At least one other phono pre used proprietary branded caps but I don't remember who.
I think higher end caps just force makers to raise prices without any real advantages in sound quality.