As I look around this thread, I see more posts about tubes and headphones than I do the Stratus. In fact, posts (never mind, threads) about headphones on head-fi.org dominate those about amplifiers. Even Dacs get more attention than amps. Does anyone else find this odd, or maybe interesting? I am at a loss to explain it....unless all amps sound the same, but headphones don't.
The tube posts, at least with reference to the Stratus are right-on, IMO. But, in my experience, the rectifier makes as much, or even more, difference to the sonics than the power tubes. Moreover, moving to a "higher grade" 5U4G type improves the sonics no matter what power tubes you are using. If I were a new buyer and wanted to spend some extra cash on tubes, I'd roll into a better rectifier, before I started to buy new power tubes.
Now let me get back to headphones. If one reads a sampling of the headphone posts on this thread, one thing stands out: many flagship headphones are fussy, fussy about amplifiers and fussy about tubes. A lot of you report that. What I don't see reported very often (if at all) is how many of these flagship headphones have users tried in their systems before they settled on one that worked for them?
So, I have a radical idea. Before people go out and plunk down $1000+ plus on the best-ever headphone, why not look for headphones that a) sound good no matter what combination of tubes you use or upgrades you make to caps, resistors, etc. and b) sound better to you (not worse) with better tubes and appropriate upgrades? Basically, what I am suggesting is that this process of tube, parts, and headphones doesn't have to be entirely a random walk, with learning in-between steps.
The first headphone amp I owned was a Single Power MPX-3 + goodies. It was a wonderful-sounding amp. and I only sold it to buy the Stratus. I started with a pair of HD650s and added K701s when they came out. No matter what combination of tubes I used on that amp, no matter how many caps and resistors I replaced, they always sounded better. The same was true of my Blue Circle SBH, to which I added a custom power supply, cap pack and then main unit, the sound from these amps never changed in character, but just sounded better. I also have a headphone amp adapter from Blue Circle to use with my tube SET and PP amps (5 of them!) and had the same experience. This was not true of the HD800 or the Audeze LCD-2, which both proved to be exceptionally fussy. Nor was it true of the newer Hifiman headphones I tried. They were all over the place.
Recently, my beloved K701s fell apart from extended use and i snagged a used pair of K7XX headphones. They are basically K701s with exaggerated bass and a bit wider sound-stage/channel separation. They also are not fussy. The same for my new HD650s.
Luck (good and bad) and common sense got me here. The common sense part was not starting at the top of the headphone price ladder. The good luck part was finding headphones that appealed to my range of sonic preferences and weren't fussy. The bad luck part was buying spending $2500 on headphones before I was able to try them in my system for an extended period. And there also something (a lot of something) to be said for improving the sonics at the amplifier end of the chain, before "rolling" headphones, something I learned from my bad luck experiences with the HD800s and the Audeze LDC-2.
In summary, to new buyers:
1. Don't buy anything or change anything internally before you have owned the Stratus long enough to break it in and learn its sonics.
2. If you have a pair of headphones you already love, stick with them for a while. You'll probably love them on the Stratus.
3. Roll the rectifier, first (even if it costs $500-$1,000), and listen on your old headphones for sonic differences. Hopefully, you will hear the differences, and they will be better.
4. The same holds true for changing amplifier parts.
5. If your old headphones + tube rolling, etc. doesn't get you what you want, then beware.
6. If ,you can't audition new headphones in your system, you may get lucky, but (again) beware of reviews. A recent Stereophile review raved about the newest Audeze cans, but already some listeners call them fatiguing!
The Stratus is an excellent amplifier, stock.
+1 - especially the part about rectifier tube. If one can afford it, the U52 rectifiers, as expensive as they may be, may make a more noticeable sonic improvement than power tubes.