Actually, the board I have impresses the DC offset on the track signal for either whistle or bell, so if it reacts to that input, it would trigger the sound.
I don't know exactly how the PS/1 processor board would be wired in, that's the wild card in my mind. If it truly reacted to motor voltage for RPM/chuff and the AC track voltage DC offsets for whistle/bell, I'm not sure why it wouldn't work. What you posted previously appeared to indicate that's the way it would work.