Mullard cv4003 & 12au7 Blackburn

the highs were too shrill and the mids a little recessed.

I've been there. Mullards are the way to go. The cathode follower does influence the overall sonic signature, but less than the front tube, of course.
I've used Mullards for gain and RCA Cleartops as followers. You get the Mullard sonic signature with some air at the top-end.

Let us know how it turns out.
Oh yeah, what did Andy say about the CV4003 tube?

I think the Primaluna stock tubes are made by Shuguang for PL.  

I've tried a ton of preamp tubes in my PL Dialogue Prem. HP integrated.  I like Ciftes, Mullards, GE military spec.  RCA clear tops are really bold and aggressive, which is fun but a bit too forward for me.  I sometimes mix a couple cleartops with Mullards or Ciftes with Mullards. 

@lowrider57 I actually forgot all about it haha. Guess it doesn't matter now. The price was way less than Upscale Audio's $110USD CV4003 and I'm sure 60's Blackburn Mullards were quality.

Mixing tubes sounds like a good way to go. Thanks gents!

Good deal, @msommers . I've bought from Andy four times and all his tubes have been of outstanding quality.

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.