How much difference will a phono stage upgrade make?


For the past couple of years I’ve slowly been upgrading my audio equipment. I currently have a Primaluna Dialogue Premium HP integrated amplifier, an EAT C-Sharp TT with an Ortofon Quintet Black MC cartridge, and Tannoy Revolution XT 8F speakers. The weak link at this point, it would seem, is my phono stage, which is a Pro-Ject Tube Box DS. All things considered, my system sounds really good to my ears, but I can’t help but wonder what a phono stage upgrade would bring to the table. I’m looking at the Manley Chinook Special Edition MK II, which is a big step up in terms of cost, but I wonder how much better it will actually sound. Has anybody made a similar upgrade, and was there a marked uptick in sound quality?
12hz
papafrgog, sorry I misinformed you. The tubes that Aesthetix sold me were JJs, not Sovteks.

Regardless, the replacement Gold Lion B759s are working wonderfully for me.
I would consider the iPhono II. I have one but recently upgraded to the Allnic H1201. Head to head, the differences were more subtle than expected (although the Allnic was green). The iPhono provides tremendous performance in a small package withlots of flexibility.
Thanks everyone for a lively discussion and lots of useful feedback. I pulled the trigger yesterday on the Manley Chinook Special Edition MK II, so I’ll be up and running with a new phono stage this weekend sometime if all goes as planned. 
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He's coming from a  Pro-Ject Tube Box DS. Could throw a dart, anything within range guaranteed to be a skin-tingling revelatory experience. Hard to go wrong with any phono stage at this level. Ought to make him very happy indeed.