I'm not going to model CFB, it is too time consuming. By definition 6dB feedback means half the gain. For triode no feedback you need 1V rms for full power (~18W for a low loss transformer). So 2 V rms for 6 dB feedback. For UL at the same power it is 0.55V rms no feedback, 1.1 Vrms with 6 dB feedback. If you bypass the CCS's for UL at the same 0.55Vrms, power increases to 24W and distortion drops by a factor of 4 (even less than triode distortion).