i've been using my AV-400 (higher wattage than the Sakura) for around 6months already, still with the stock tubes. No plans of tube rolling since i'm very happy them and i know that this not really a tube amp, not even a hybrid. But it belts out clean and loud music i have no complaints. Aside from the modifications on the unused pins of the driver tubes and bypass caps that Sir Tony did no other mods or upgrades were done. Very satisfied with it, alternating with a vintage Phonola 6AQ5 tube amp
Just use it as it is and be contented. And read the the whole thread even if it's long, you'll learn alot about this amp