I am a Dude owner as well and will add my two cents.
Vandermeulen, your comments are helpful and stimulating IMO. It is an argument you hear about audio in general. Distortion is a part of audio whether we like it or not. Bob Smith at SpTech (now Aether Audio) told me at length about the levels of distortion in speaker drivers and that no one really likes to measure it since it is so horrific. I have personally battled some level of distortion via cables, the room, digital sources, etc. As far as preamps are concerned, the question is how quiet is it, what is the nature of the power supply (how stable, etc), and do you like first order harmonic distortion via tubes. I confess that I like tubes and have always had a tubed pre in the rig. A lot of older recordings used tubed microphones, etc and smoke a lot of digital offerings of today. As far as the Dude is concerned, it is dead quiet, dynamic, with jumbo sound staging, etc. The power supply is a proprietary tube regulated affair that is very stable. You can alter the sound of the Dude by tube rolling. I have landed in NOS RCAs currently.
Gary, it sounds like you already have a tube bias. Depending on where you are, you could potentially demo a Dude. If you live in NC, you most certainly can.....Charlotte.