msommers, Perhaps I shouldn't write this, since you've already spent your money, but IMO the best sounding 12AU7/ECC82/CV4003 is actually a 6CG7 (in 9-pin miniature format) or a 6SN7 (octal base). Neither of these tubes is in the 12AU7 family but both of them exhibit the electrical characteristics of a 12AU7 and can be substituted, if you know what you're doing with the tube socket. You just have to fiddle with the filament connections vis a vis the 6CG7/6FQ7. 6SN7 would take a lot of work and probably is not an option.
Amperex 7316 is not exactly a 12AU7 but can be installed into the same socket with no mods and is close enough electrically that there are no problems. Nice tube, too. I admit I have a bias; I have never liked the 12AU7 in a gain stage. OK for driver or phase splitter. If one must, I liked the Amperex Bugleboy Ecc82/12AU7 best amongst a bunch of others I tried in a gain stage, back about a decade or more ago. Real Bugleboys are scarce now, sadly.
Amperex 7316 is not exactly a 12AU7 but can be installed into the same socket with no mods and is close enough electrically that there are no problems. Nice tube, too. I admit I have a bias; I have never liked the 12AU7 in a gain stage. OK for driver or phase splitter. If one must, I liked the Amperex Bugleboy Ecc82/12AU7 best amongst a bunch of others I tried in a gain stage, back about a decade or more ago. Real Bugleboys are scarce now, sadly.