Adding a Korg NuTube buffer to solid-state chain – bias & polarity tips?

[Forever25]

My current front-channel chain is Apple TV 4K → Rotel RSP-1576 Mk II (Dirac/DSPBypass) → Odyssey Kismet monos. The system is clean (<0.3 % THD at 80 dB SPL, measured with REW), but I’d like a touch of “tube-ish” H₂ warmth without changing the frequency response or bass control.

The First Watt B1 Korg NuTube looks perfect: unity gain, low Z-out, user-set bias.

1. Bias sweet spot – People quote anywhere from 10 V to 18 V on the NuTube plates. Where does H₂ sit ~0.4 – 0.6 % (with H₃ at least -20 dB) and which side of the 12 V “phase flip” do you prefer for stereo depth?
2. Absolute polarity – The buffer inverts; do you guys flip speaker leads or add a second inversion stage? Any audible downside to leaving it 180° out?

Goal is “season to taste”: be able to dial the bias or bypass the buffer and land back on the original Dirac calibration unchanged.

ALSO: If anyone with a finished build wanting to sale please DM me!