Doge 8 Clarity: 12AT7 replacement for phono stage

Hello fellow enthusiasts... My apologies in advance for the noob question.

I've put together my first all tube system, as far as preamp and amp combo is concerned. Looking to see IF replacing the phono section's 12AX7 (Mullard ECC81) tubes with lower gain 12AT7 in my Doge 8 Clarity 2017 ed. will help lower the "hiss"/ tube rush coming off with my current set up. Doge's phono setting is on MM (using Bob's Device Sky 20 SUT), Phono: 47k, tried both normal and low sensitivity, (- 8) gain reduction, but "hiss" is still audible from my seat 7' away from the speakers. 

I'm looking at replacement tubes from Upscale - Mullard 6201 which they claim to be the "quiet" ones. Not sure if it will help in lowering the hiss I've described.

Doge's line level still holds the stock 12AT7 tubes and to me - they sound nice as the reviews online says. I'm sure it can do better with tube rolling. No audible hiss from my seat. Switching between any line level onto phono input clearly augments the hiss.

To take advantage of Doge's much improved line level over the phono, I've utilized my only external phono stage - Schiit Mani. Not ideal but i can handle that better than deal with the hiss using the Doge's internal phono stage. I've contemplated on just upgrading to a nicer phono stage but that's another topic.

So, will it work to replace the 12AX7 with lower gain tubes 12AT7 to decrease hiss in my system? 

Thank you in advice for your time and responses.

Current system:
Rega P3 (2016), NEO ttpsu, DV 20X2L
Schiit Mani to line level vs Bob's Device Sky 20 to phono level
Doge 8 Clarity 2017 ed.
Mystere PA11 
KEF R3 on stands

@ atmasphere: I appreciate your input and guidance. I know you're well respected in these forums. I will do the test you recommended I do, and will report back.

@ mulveling:  Thank you for the valuable tips in increasing signal to noise. Looks like I will have to really look at a good set of quality, quiet, MC phono grade tubes compatible with my Doge 8 to properly achieve my goal. 

@ robertplata: Splurging! Yes, and as mentioned above, I will have to pony up for the "right" tubes. 

I'm glad I posted this question of mine, as I was ready to pull the trigger on some tubes that I would have not been able to return. That would've been an expensive experiment. 

I have two 1960's era Telefunken blue tip medical grade 12AX7 tubes in my phono stage that I got from Brent Jessee about seven years ago. $350 for the pair in 2012 but are very nice. Using with Ortofon 2M Bronze and am quite happy with this setup.
I own a doge 8 and the phono section is quite good. I use it with a Hagerman piccolo 2 step up, a very very good one for peanuts. I have no hiss with a Benz lps.
In the phono section I use a Mazda silver 12 ax7  and other make of tubes. The man in charge of after sale service in europ who is a tube specialist recommend electro harmonix as a good cheap tube which work well on it.
@oyie2000 and gilles130, 

I have a Doge 8 Clarity the 2021 edition.  I, too, have hiss in the otherwise magnificent sounding phono stage.  I've swamped some tubes that aren't noisy in other preamp stages (but not phono).  

I really want to resolve this issue because the phono stage is not an afterthought in this product.  It has it's own preamp section of all tubes (no OPAMPs--not that those are bad).  It is rivaling my Manley Chinook and if I can ditch the hiss, I can sell the Chinook (which is awesome) and reduce things by a box. 

The hiss is constant in power, volume, etc.  It sounds like super pleasant but loud white noise.  It has a “shhhhhhhh” sound that is constant with no electrical variance, buzzing, etc.  Just smooth and very loud. 

Now, as atmasphere indicated, the hiss goes down a bit during play so maybe I can just live with it.  

I think I've tried all sorts of loading to no avail.  I sent an email to Marc with Doge.  Let's see what he says.  This is a great product.  The line stage is super!