According to the C26 Manual http://wegavision.pytalhost.com/McIntosh/C26_own.pdf
SPEAKER SWITCHES
To switch the main and remote stereo speakers using the push buttons on the front panel, the power amplifier output leads must be connected to the amplifier output terminals on the rear of the C 26. The main speakers must be connected to the main speaker terminals and the remote speakers to the remote speaker terminals. If either main or remote speaker button is pushed to OFF, load resistors are automatically connected to the power amplifier to compensate for the speaker.