Nothing I’ve heard has a sweeter tone than the HA-300 and Susvara combination. For gentle and elegant music, like vocal and acoustic pop, it’s unbeatable. For punchier and harder slamming music like EDM, bass-heavy pop, dance, hip hop, R&B, and rock the HA-300 and Susvara aren’t the optimal match.
The Susvara scales with more power like no other headphone I’ve heard. With enough power, you can make the Susvara slam almost as hard as the Abyss 1266 Phi TC while retaining all its strengths. My little SMSL SA-400 Class D integrated amp easily beats the HA-300 with the Susvara for harder hitting music genres and cost me less than 10% of the cost of the HA-300 with upgraded tubes. The gain in dynamics and slam is worth the dial-down in sound stage, clarity, three-dimensionality, and tone.
I prefer the Abyss 1266 Phi TC with the HA-300 than with the SA-400 for full-on music genres though. You still get plenty of slam and dynamics with the Phi TC and HA-300 combination, it’s not worth losing the beautiful tone of 300b tubes. When you speaker tap amp the Phi TC, it can be too much and not in a good way. The Susvara is technically stronger than the Phi TC and just keeps scaling.
The relative weakness of the Phi TC are hollowed out mids and that’s where the HA-300 excels. AndyKong wasn’t convinced about the synergy of the TC drivers with 300b tubes. I like it, the Phi TC adds what 300b tubes struggle with, dynamics and slam, and the elegant and refined HA-300 makes the Phi TCs sound less ragged and more grown-up.
To me ears, tube rolling the HA-300 just improves it’s incredible tone and refinement, the basic sound signature doesn’t change that much in comparison with switching between Susvaras and the Phi TC or from a tubed HA-300 to a solid state integrated amp like the SA-400 from the speaker taps. If you have very diverse tastes in music, you might be better off with the SA-400, or something like it, than another pair of tubes.