I have a Passive Slagle AVC as a standby Pre-Amp and have had a DACT and a DIY built Passive Stepped Attenuators on Standby as well.
All of these have been coupled to Valve Input/Output, Valve Hybrid and SS Phonostages.
My experiences has been that these types of Standalone Volume Controls when used in my system, are presenting a colour/deterioration to the SQ to varying degrees of being noticeable and can become detractors when detected, and as a result are not my daily used devices, as I am attracted toward a SQ that is transparent.
With your Power Amp being Class D, it might take a few demonstrations of differing Pre Amp Types along with your Phon' and Power Amp's before the marriage of the devices offers something to really satisfy your tastes.