I think the owners all congregate over at Audio Aficionado. You gotta pay to use the forum but it is the best place to see what he is up to. Dennis reads all of the posts there and some of his tech partners are there too.
The choice to use the WE 300b is a great example of how he selects the components to use. He tunes the amp to a sound and uses the parts he needs to get there. You can see some fancier caps in some of his other amps but he only uses them where he thinks it will make a positive difference. Fancy, more expensive parts are not objectively better in every case. Some folks get the idea that it is the parts that determine the sound when in reality it is the entire circuit. It is much more important to “tune” the amp and use the parts that get the sound you want. Mick from Supratek will customize builds for you but he won’t change the components he uses. He knows what his preamps sound like and the reputation they have built. He won’t build with boutique parts because they make his preamps sound different but not necessarily better. He can stand behind his design and the sound quality of his preamps but he doesn’t want to send out something that doesn’t sound like the rest of his gear. Dennis has been making 300b amps for over 50 years and is intimately aware of the different compromises that go into the sound of an amp. Like Mick, he builds to a sound
But speaking of compromises, his current round of amps have fewer of them because he is doing it for fun. He is retired and does not depend on amp sales to make a living. They are a labor of love for him. He says the current amps are the best sounding he has ever made. I believe him. Mine is certainly wonderful:)