Are Pre-Amps necessary?

The Russian euro15k Wagner Audio Dream Dac dac also uses this volume system for going to poweramp direct.
https://www.monoandstereo.com/2016/06/wagner-audio-labs-super-r2r-dac.html

Cheers George

Have had Burmester 001, DCS Puccini with clock and now Burmester 089, which all can drive amps without preamp and in every case prefered the sound with preamp (Burmester 011 and Arc Ref 3)

George, not sure where your list of "all those preamps" came from but of those, the Khozmo (i.e., Hattor) is the only one I have owned.  I do own McCormack's TLC-1 passive/buffered stage that Steve has upgraded to a much higher level that he calls  "very close to my VRE-1."  When I owned that Metrum Adagio DAC with internal VC, I modified the TLC by taking the Shallco VC switch out of the circuit (replaced it by soldering two AN Tantalum silver resistors to the board) thus turning it into a unity gain buffer w/o VC.  I did that because, to me, the Metrum DAC sounded noticeably better with the active buffer in the chain, even though the DAC output 4V.
I have since moved to Mojo Audio's EVO B4B 21 DAC, which does not have a VC so I added the passive Khozmo unit, which provides remote VC, balance control, and a nice visual display.  I have tried running my system with just the Khozmo passive unit but I much prefer the sound with the TLC active buffer also in the playback chain. 

That list came from a post you made a while back.
You don’t use a Metrum Acoustics Adagio dac now?

Also understandable that you preferred the active buffer as the Khozmo, and most tube pre’s would not have suited the 10kohm input impedance of the SMc monos.

Cheers George