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
I agree with Stevecham's assessment of the Rhea, concerning low level tube rush. But, after 12 years I upgraded my unit to the signature version. Oh, what a difference. Overall a great improvement and a much lower noise floor. The virtues of the Rhea, flexibility and the ability to adjust load and gain from your listening position, became more evident, as I upgraded other sources in my system. Simply musical in either configuration...
I was using the tube box ds as well and my problem was low output ,rega rp 8 ,alphea mc cart .i purchased a used Mac mc100 and wow that solved my problem! Mac 601 mono’s, focal 1038 be.
I managed to find a Herron VTPH 1, here on Agon, and after hearing so much about it, I picked it up.  It blew away my Fosgate and took its place.  I wrote Keith and asked about trading in the VTPH 1 (mm only) for the 2a; he offered me a credit that was exactly what I paid for the '1' so he built a 2a for me.  With my Rega RP10/Apheta2 connected, the music was glorious.  After about 2 months I notice a static like noise on the right channel.  I contacted Keith after doing as much troubleshooting as possible to isolate it the 2a.  He asked me to send it back, which I did.  He could not hear the same noise after listening for a week.  And this next part is why I will never have another phono stage except a Keith Herron designed one.  Keith, without being able to duplicate the noise, decided to build me another 2a rather than return my original.  Yes, that is correct, Keith Herron built another 2a for me and kept my original.  Further investigation, on my end, found the static noise was caused by an external source (computer power supply).  I have been in audio for 55  years and I have never had any manufacturer treat me so well as Keith Herron.  He not only makes the best phono stage, but he is also one of the true gentlemen in this business and that means quite a lot nowadays.
Well I'll put my experience out there. .I have a cary sli80 and upgraded my turntable to a vpi clasic 3 witch I really enjoy. .tried some expensive tube phono stages like rogers pa1a and don't think it's worth the asking price.I'm currently using a rega aria and getting the results I was looking for. .with that said the jc3 from parasound is really nice and there are some good prices on used ones as well..best of luck. 
Well I'll put my experience out there. .I have a cary sli80 and upgraded my turntable to a vpi clasic 3 witch I really enjoy. .tried some expensive tube phono stages like rogers pa1a and don't think it's worth the asking price.I'm currently using a rega aria and getting the results I was looking for. .with that said the jc3 from parasound is really nice and there are some good prices on used ones as well..best of luck.