I laid out a similar circuit on my bread board that was a hybrid between the one above and the circuit diagram (MX-830 HCA) for the BA3122N. It rang out similar but a bit off on the diode test between pins 1 though 9 (72 combinations). My breadboard connections are not stable enough to try in the MX-2 left channel. The next step is to make a prototype circuit board and try it out, but my efforts have stalled since brutal very generously traded me a replacement BA3122N. This is a fairly pricey possible solution, the four dual transistors alone are at least twenty dollars and are becoming hard to find.
I didn't have any success with Alibaba, they list them but when I inquired they were all out of stock.
Possible donor units that use the BA3122N ICs are: AX-730; AX-930; AX-1050; AX-1070; AX-1090; MX-2 & MX-1.
According to Yamaha USA the MX-1 was on sale for twelve years until 2005 and brutal had hard time getting this chip in 2011. What a shame!