I've had a few Wadia's, and depending on amp pre-amp and CD model, my preferences have varied.
The 830 I had for about a year and preferred it through a BAT VK-50se pre-amp - amps were McCormack dna-1 rev A mono's. Direct, the soundstage was too flat and highs were hard.
The 302 for about 6 months and preferred it direct into my Classe Omega. But could go either way (tried an Audio Valve and a Lamm, forget the model, also a demo with a placette passive), there were equal trade offs. Direct was a little hard on top but not as much as the 830 into the McCormacks. The pre's added noise and distortion but added some air and softness. Passive may be the way to go if you must do a pre.
The 861se for about 2 months, and clearly preferred DIRECT. The soundstage can be 3d, the images are thick, each drum sounds unique and the air pressure from kick drums feels like you are there, and the bass detail is stunning. I never considered putting it thru a pre given my experience with them and the 302.
The 270se 27ix combo - same thing as the 861se and then some.
With the TOP Wadia units, everything matters and makes a difference, amps, cables, platforms, cones, etc. These things matter on all system I assume, but the changes are very dramatic in the 861 270 27 units. Things can range from warm to hard, resolved, musical, punch, finesse, detailed, relaxed, etc. I tried the 861 at a friends house and my unit sounded polite, but we added a beefier PC and she started to get a little attitude, then we bypassed the pre and things opened up. Everything matters, because these things put back exactly what you give them.
I need to be below 70 on the units before I notice any degradation, however, I know my Andra speakers are a completely different animal depending what volume you run them at, too low and the music looses some evenness and dynamics, so I do not know if the performance at lower volumes is the Wadia or the speakers.
I don't think one system can be great in all areas at all volume levels. My critical listening is at near live performance level, that is the volume I want my system to sound best at. Less than that, any system will sound un-realistic - maybe clearer, with some dynamics, but not realistic.
My music preferences are acoustic and electric Jazz and rock, with some classical and the kitchen sink.
I will be trying some external volume attenuators that hook directly to the amp's input and, the IC's go directly to the attenuators. If these do not interfere with the magic at real volume levels, and make the lower volumes "better" too, then I may have it all? If that happens, I will sing the praises of the person building them for me.
Many variables and preferences. Direct has always (other than 830) brought me closest to the music.