Dual Mono is a real pain to bias since R + L ch. PCBs are stacked on top of one another, necessitating unscrewing the top R ch, lifting it up gently, and biasing the bottom board with magnification and bright lighting. Sonically, the amp sounds less bright, a welcome change. Heating issues are resolved too. However, the soundstage is a bit smaller now, and some of the 3-D magic is gone. Perhaps it's due to the flatter response?
Before Biasing: R ch: 32mV, 34mV. L ch: 29mV, 28mV
After Biasing: R ch: 21mV, 21mV. L ch: 21mV, 21mV
Germay, you're the man!