Amplifier speaker relay problems.

I'm not familiar with the circuitry of your amp but I suggest checking more deeply arround the ciruit board for the following possible failures:

This relay faliure can be on more reasons than you might think of. Relay can also block an input stage thus blocking any signal that is about to enter the blown output stage.

I'd suggest checking output devices since often fuses can act too late to protect and Relay is acting only after the output stage is blown. Please note that relay in this case shunts the signal(and/or power supply to the output stage) through the load resistor and depending on time of such task can also be blown along with load resistor.

To check your output devices remove relay to connect directly and use dummy load 50W/10Ohms resustor to MEASURE DC from the binding posts. You can end upto 30V that can blow the speaker in the flash even after you replace relay wihtout checking out all possible failures.

Possible reasons for output stage failures:
--Bad trim pots that adjust the emitter(or channel) bias.
--Surge or voltage jump(s).

You can do much better without these relays and opt for smaller output fuses i.e. .5A instead of 2A. Thus you will increase resistance on the signal path but along with that elimintate the switch that impacts synergy much larger.
You can get high quality ceramic fuses from www.mouser.com for pennies.