@DisalvoA992
Each triangle is a power amplifier. Let's start by reminding that the Mentor is a dual mono amplifier and not balanced. It accepts single ended and balanced inputs and delivers a single ended output. The 4-pin XLR plug is for convenience. Not balanced output.
So in a single Mentor you have left and right channels amplifiers each one with its own transformer and power supply.
Dual Mentors are a fully balanced configuration.
One Mentor is the amplifier of the left channel and the other of the right in a balanced mode. So we have four power amplifiers. (Four triangles)
Left Mentor amplifies L+ and L-. Right Mentor amplifies R+ and R-. Each component of the stereo signal has its own transformer and power supply. Four of them as a whole.
Left Mentor delivers L+, L- and ground in a 3-pin XLR plug. Right Mentor delivers R+, R- and ground in a 3-pin XLR plug.