Another Cronus Magnum question

My Cronus Magnum integrated has the Tung Sol KT120 output tubes and a Mullard CV4003 tube for the preamp section. I am still using the stock 12au7 tubes and the 12at tubes. Changing the preamp tube made a big change for a more ripe midrange which is what I wanted. What advantages would there be to replace the other 4 tubes to something better?

If I do change the other 4 tubes, can anyone give me some recommendations? I don't want to spend a fortune, but I assume there are much better tubes than the JJ tubes in there now. Anyone?
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I thought I would revive this thread. I put a NOS Mullard CV4003 (12au7) tube in the center position for the preamp and 2 Mullard 12au7 reissue tubes for the drivers. For the splitters, I used 2 Svetlana 12ax7 tubes. The amp sounds more open now and it is far better than the stock JJ tubes.
I have a Cronus Magnum as well, I've tried different NOS tubes an ultimately settled on the following:

Preamp - Cifte 12AU7
Section Drivers - Mullard CV4003
Phase Splitters - Raytheon 5751 w/Windmill getter

I've also had a Mullard CV4003 in the pramp position, but liked the Cifte better as I felt the soundstage was more 3D.

Changing out the stock tubes really improves the sound.

How long have you had the amp and how do you like it so far?
I bought the amp used in late August. It was 6 months old when I received it. The amp replaced a Classe 175wpc power amp and a Modulus3A tube preamp. I like the Rogue integrated much better, especially now with the updated tubes. This integrated is in my secondary system which is in my home office. I listen to it 8 hours daily with absolutely no fatigue. I may change the speakers to something more efficient like ZU Audio or something similar.
I also have the Mazda Cifte in the pre-amp position. It's flanked by late 50's La Radio Technique 12au7's and Mullard 4004 12ax7's.

Really nice sound from this combination.
I definitely agree that the amp is very easy on the ears, I can listen for hours without any fatigue.