Hi Britishbane,
Much as I'd love to sell you a Serac turntable, I agree with Raul.
You can learn quite a bit about setting up your current rig, while shifting your focus to your electronics.
I'd seriously look at an amplifier and line stage upgrade (perhaps a high quality integrated?).
In stating this, I'm assuming that your Pro-ject tube box is reasonably competent, and is the strongest link in your electronics chain.
You know how all of this goes however ... soon your Pro-ject will be your weakest link. Welcome to the club (grin).
Amplifiers and speakers are so related, that it's best to think of them as a single component.
I don't have recent experience with amplifiers that mate up well (musically) with mid-efficiency monitors.
Yesterday, I heard that of Nick Doshi's tube amplifiers is for sale here on the 'gon. Search on "Nick Doshi".
I have no commercial interest in this, but know that these amplifiers began their life as classic European made units. Nick sources them for the high quality of the output transformers and implements his own design around these chassis.
They're good for an honest 50 TUBE watts, and unless listening to metal is your prime source of entertainment, they ought to do just fine.
The hip thing about this strategy is that this amplifier could become the cornerstone of your system for quite a few years to come.
The only problem I see with this is that you'd also need to find a competent line stage.
I'd seriously look into this approach (even if the Doshi unit has sold), but that's just me.
Cheers,
Thom