The speaker relay is the black box, marked DEC DH2TU 24V 3A, near the speaker connections. It's not necessary, but if you want to see this relay, you need to remove the top and side PCB by removing 2 screws joining the side PCB to the main PCB.

To get access to the relay's soldered pins, you need to lift up the largest printed circuit board (PCB). This is done by removing 5 copper coloured screws from this PCB (note: one is hidden under the fan assembly).

Further disassembly details can be found in the online RXE100 service manual page 6. Check that the relay's coil voltage between green arrows is zero volts in the non-working condition ( 24V when working properly), check you have not left the headphone jack in.

If you have 0V between the red arrows, this explains why you have no sound from the both speakers. The work-around here, at your own risk, is to solder a wire between the green pins and another wire between the blue pins.

Both speakers should now work. You may notice a slight thump from the speakers when turning on and the speakers will not mute when you plug in headphones. But these are minor problems. ps Perhaps don't do this repair if using your prized speakers as they will have less protection against future amplifier faults.

Now the speakers are working you can check the dc bias across each of the speaker terminals and subwoofer. Mine were satisfactory at <10mV dropping to 0.5mV after a few minutes

Internet guidance suggest dc bias below 50mV is acceptable. Above this you may get distortion. If above about 600mV may cause damage and would be why the protection circuitry is operating, in which case remove the soldered-in wires and find a repair for a dc offset fault.