Igor - I love your approach of introducing just one variable at a time - it's one I intend to follow as well. I think too much too quickly and it's hard to tell what is doing what.
Bang for buck is a good way to go. I've wondered if it's something of a "waste" to be using some of the finer NOS 12au7s as rectifiers - I guess it depends on the effect and the JANs would be a great way to test that.
For the WA7 Most have said stick the EH in right away, so I bought them at the time I got the amp too, but like you i'd like to get to know the stock Sovteks first - partly because, as I understand it, those EH Gold Pins are no longer in production, so unless another manufacturer takes up the mantle. (which they might), they
will run out eventually. Who knows how many Woo has - maybe enough for all of us for the foreseeable future. I've also noted that not
everyone prefers the EH, although most seem to.
It's my first tube amp too so I'm really excited about trying the different combinations and having a slice of history in there to supply the magic! Since you are tuning the sound for the HD800 and me for the LCD2 we may well be wanting to do different things but it'd be great to hear how you get on.
One pair i'm looking forward to trying are these that I grabbed for a good price via Ebay: they are new production Psvane 12au7s, gold pins. I thought it would be good to see how some of the new offerings fair. I need to check compatibility - I think all 12au7s can be used but not sure if there is any variation in spec.
Best of luck!
Jeb.