To clarify a few things:
1. Tube swapping absolutely *does* change the character of the sound. As Skylab said, we're using the tubes for voltage gain--arguably the most important aspect of the overall sonic character of the amplifier--so yes, changing tubes will change the sound quality. Sometimes dramatically.
2. And yes, we encourage everyone to tube roll. The operating point is set by a current source, so there's no danger in trying many different brands of 6DJ8/6922/7308/ECC88/6N1P. The catch is: make sure you get the tubes as perfectly matched as possible, and buy them from reputable sources. We've been bitten by funky/nonmatched/microphonic tubes from sketchy sources from time to time. The other catch is--yep, we'll admit it--the tubes are kinda fun to get out of the chassis. Hint: use the foam provided with the tubes to grab them.
3. The JJ tubes we provide give good overall performance when sorted and matched on a modern curve tracer (NOT on a 50-year-old tube tester with a single meter), and they have the added benefit of being non-microphonic and having good heater/cathode alignment for low noise. They are used in $2500 amplifiers. Are they the best thing out there at any price? Nope. That's why the amp is rollable.
4. Purrin, I'm unsure how you got the impression Lyr is dark or closed-in, though I don't debate it. What I will say is that you're the only listener who's said that. To date, that is. We'll see what happens when more impressions show up.
5. The more I hear about dark/smooth/etc, the more I remember the Theta/Sumo days, when it was a near-nightly occurrence to head over to the Theta listening room (Sumo and Theta shared an industrial park.) And--it's funny--every single one of the best amps sounded "quiet," "dark," or "closed-in" on initial listening. Every time we reduced feedback, the amp got "quieter" and "softer." Every time we improved the open-loop linearity, the amp sounded "quieter" and "rolled." And yet those amps measured ruler-flat into the AM band. Aaaannnd . . . on longer listening, every one of those "quiet, rolled" amps proved to be more accurate and ultimately resolving than the amps that sounded detailed and bright on first impression. But hey, that's my story, right, and I'm an evil manufacturer bent on emptying your wallet. Or something like that.