Tube Pre-amp Suggestions.

@kds 

I wouldn't know about that as I have no experience with class D, or specifically, Purifi amplifiers.

@kds  if the budget is $3000, get this Tube Preamp. Get the 6SN7 tubes - https://www.schiit.com/products/freya-f

And for monoblocks of the Purifi cloth. HELL YES.

Get two monoblocks from Buckeye. This is the top of the line Eigentakt Module - https://www.buckeyeamp.com/shop/amplifiers/purifi/1et9040ba/monoblock

I use Purifi Eigentakt Monoblocks in my MoFi Sourcepoint 888 setup and the damping factor means the control of transducer is seamless without any sag or lagging. Incredible headroom with wire on gain performance

Another vote for a BAT valve option, used if necessary. In my experience they walk all over price-equivalent Audio Research options. Much better soundstage and dynamics. 

Is a remote needed?  Also, are you using balanced interconnects?

I know you said “tube” but the matching Coda Continuum CB preamp is excellent and retains the smooth tube-like presentation of their amplifiers. I’m a Coda dealer and have one ready to ship if you are interested.