Sabaj PHA3 and HD6XX, Anybody?

So, a friend turned me on to the Sabaj PHA3 a couple of weeks ago. It was on Amazon for $27, where it is now selling for around $39. The great part is that it features a pair of E180F (6J9s in Chinese lingo)/6688 tubes in the signal path, albeit hybridized with some transistors on the input stage. Well, I listened, and heard tube things happening, and wanted to know what it would sound like with my HD 6XXs. And, so I bought one. It sounded pretty damned good for a $30 amp. And since it is really just a circuit and the tube does the sound work, I wondered how much better it could sound with NOS tubes. First up, I found some Amperex manufactured Phillips E180Fs ($25 a pop), probably from the 70s, Holland manufacture. I ordered them. And Holy shit. It did amazing things to the midrange. Textured, warm. Lovely sound. Well, I have been hearing about the glories of Mullard tubes. So I scoured the internet for Mullard 180Fs. Found 'em on Etsy, of all places for $30 a pop. They arrived today. I spent a moment listening to the Amperex renditions. Then I put in the Mullards. And the sound went from rich and warmly mid-range focused to broad-spectrum-linear with tube sparkle and air. This is my first foray into tube rolling, and I’m sold. On to my question to start the discussion. Has anyone tried this little amp yet and what is your take?