When you write "all three fuses" I assume the tower amplifier has three 25 amp fuses for example.
Most amplifiers have internal circuitry to protect the amplifier from being damaged by low or over voltage, a damaged speaker, or a shorted speaker wire. This protection circuitry normally engages long before the fuses would blow. The actual music demands typically do not approach the amplifier fusing. When the fuses blow that usually means something serious within the amplifier is in need of repair. When the amplifier is bad it may blow the fuses without speakers being connected. If you smell the burnt electronic odor coming from the amplifier then that's pretty conclusive. Your amplifier needs repair. If you sense the same odor from the speakers then damage has probably began there also. Don't repair the amplifier without thoroughly checking the speakers too. Problems are often related. At minimum, check the DCR of both speakers to make sure they are consistent between the pair and meet factory spec. A 4-ohm speaker will generally have a DCR between 3.5 and 4-ohms.
Damage can be accumulative (such as thermal) or sudden (water for example) so you really can't narrow it down to a time or event.