i can tell you, at least from my experience, the lower level Audio Note UK is fantastic and superior to many other similar components at their respective price point. Where things really jump to the next level sonically is with the Oto SE (which i believe is a level 2) amp. the harmonic texture, bass performance, sheer refinement and musical involvement of the Oto SE is simply incredible and punches way above its price point. indeed, there are other musical amps out there but if you want the best, at every respective price point, i cannot think of another manufacture that does it better then Audio Note UK.
As you go up the Audio Note UK levels they certainly do use better parts (just as any manufacture does) but they have many different circuit designs. they have amp designs that use valves ranging from the ECL82 all the way up to the 211! but yes, several of their finer amps do share the same circuit but use different materials in the transformers. for example, the Jinro integrated (level 3) (and I believe is one of the finest sounding amplifier on the planet) uses copper in the transformers, while the Tomei (level 4) uses a mix of copper and silver, and the Ongaku (level 5) uses all silver throughout. but the circuit design in these amps are the finest sounding in the world.
they make relatively affordable components and they make extremely expensive products, just like many other high-end audio manufactures. what Audio Note gets right and distinguishes them from other manufactures is they actually listen to their products, they don't rush to produce something ... they wait until they are confident they have designed or improved upon, they stick with what works and sounds the best and then work tirelessly to improve and perfect that.