As to alternatives, well. I just did a back to back with the all Sylvania Mil-spec and the phillips/Lorenz and I really cannot tell a difference between the pairs which bodes well as those old Mil-spec Sylvania's do come up for sale quite often. I cannot emphasize enough though that the Mil-spec Sylvania's are very different beasts to the non Mil-spec ones that come as standard with the amp!
For me, having heard the stock Sylvania's the Mil-spec ones came as a very big surprise. I had all but written off the US made tubes as none really did it for me the way the European made ones do but these are exceptional and I feel confident in recommending an all Mil-spec Sylvania set up as an equal alternative to the Lorenz/Phillips combo
I think If I were to boil it down those two pairings are my top two, followed by Phillips/Siemens (the Siemens is such a beautiful airy and detailed tube but it does benefit from something a bit more weighty to underpin it I feel and the Phillips do that, as do Mullards.
For sweetness then Radiotechniques are my next favourites .