Tube advise for Aesthetix Callisto MKII preamp

Hi there,

I just bought a used Aesthetix Callisto MKII.
It was well burned in so I started tube rolling after a couple of days.

So far I have replaced the following tubes in the main unit:
- Stock sovtek 6922 for Amperex white label USN
- Stock sovtek 12AX7 for Sylvania 5751 gold label
black plates

The improvement I got was not subtle, things got warmer more vibrant with greater dynamics and detail, like a veil was removed from the soundstage.

Only drawback is that noise levels increased a bit but still low and more than acceptable to me.

I am now ready to start replacing the 12AX7 and EL34 on the PS and also the 6SN7 on the main unit.

So my question is:

- Is there a problem changing all the the 12AX7 tubes in the Callisto to 5751?

Although I love the 5751 black plate Sylvanias and also the GE, I understand that the 5751 tube has 70mu and opposed to 100mu of the 12AX7.

Thanks a lot for your thoughts.