Hi, I have the Mastersound PSE and I've done a bit of rolling recently. I've purchased 4 new Sophia princess carbon plates which were a dramatic improvement over the standard Electro Harmonix tubes. If I did it again, I might try the Sophia mesh-plates as I find the Carbon plates to be a bit 'polite'. I was looking into the Shugang Treasure 300b tubes but, ultimately decided on the Sophias.
I've recently switched out the 12AU7 pre-amp tubes with NOS Mullards. These tubes now have 20 hours on them and are starting to open up. Swapping out your pre-amp tubes will yield changes in soundstaging, imaging and realism of human voice.
Cheers,
Bryn