Obviously, no storms, surges, nothing strange happened.
As for voltage surges how would you know? Not all voltage surges are caused by storms.
I notice the input voltage rating for the amps is 115Vac.
What is the avg mains AC voltage at your residence? Is it stable or does it fluctuate?
Does it ever get above 126V?
What was the voltage at the mains power receptacle outlets the day you powered up the amps and the AH fuses blew? I doubt if you know...... Who checks such things.
Am I defending the Audio Horizons fuses? NO. Just giving the guy at AH the benefit of doubt.
Just a guess the 5 amp OEM slow blow fuses that came with the amps have a longer lag, delay, time than the AH fuses.
If the amps are still under manufacture warranty you might want to check with the manufacture about using aftermarket fuses in the amp, in place of the OEM fuses that is spec’d by the manufacture. Especially tube amps.
Use of any other than Rogue Audio factory parts may void this warranty.
http://www.rogueaudio.com/documents/ApolloManual.pdf