Tube & other upgrades for Conrad Johnson pv10 pre

Well, I recently acquired a cj pv10 preamp, essentially for the phono preamp. It has a long reputation (here and elsewhere) of providing a classic CJ warm tubey sound at a reasonable price point for those of us who can't budget $1,000++ for such things. Mid-fi territory, I know.

I bought the pv 10 hoping it would offer an improvement in sound quality from the Rega Fono MM preamp I'd been using previously. It wasn't a giveaway price: people really do bid on these things on the 'bay. Everything is working and looking just fine, but...

In my initial a/b comparisons of the two phono preamps (using Joni Mitchell's HEJIRA as my test lp), I am having a hard time telling much of a difference between the preamps. I have the pv10 volume at about 9 o'clock (much louder means distortion, which the Rega would never do). I move around the speaker cables, as directed by CJ, to deal with possible phase inverting issues (not relevant, it seems).

I haven't yet checked the tubes (which I'm told were replaced at CJ factory by prior owner) but everything sounds mechanically ok.

That said, after more a/b work, I'm already wondering (already) about possible mods or upgrades. Any ideas about tube replacements that might take this stock pv10 to a higher level? Or is it all about the caps, etc? The CJ factory sells replacement tubes, but this one already has those and they are working as they should. It's just not bringing the magic yet.

The tube complement is 2x 12ax7; 2x 12at7; 1x 5751.

My goal is for an upgrade of warmth, richness, midrange "bloom," and sonorousness for small group acoustic jazz (mostly) and also seventies soul and hiphop vinyl. I'm finding the sound a little bit thin and even reedy. I want the acoustic instruments to sound more woody and more resonant. I want to hear some of the depth and skin of the bass drum. (I'm already using a REL sub to get more oomph in the bass at the lower freqs.)

The system is what I hope qualifies around here as intelligent and gently used mid-fi:
Rega p3-24 table
Linn Classik SS amp (replacement Rega fono MM preamp)
Vienna Acoustics Mozart Grand speakers
REL t3 sub
assorted ICs and cables: Van den Hul, Linn, Audioquest...

Any thoughts? Pointers?

Please refrain, if possible, from saying "dude, you shoulda spent $1500++ for a really high quality tube phono preamp." I would if I could....