Why did my amp just crash and burn ?

Hey, you may have a short.  Disconnect the cables from both ends and measure the resistance, should be infinite. Check for even the thinnest of stray copper threads.

With solid state amps, the most common cause of problems like you reported would be accidentally shorting out the  amp by touching the two speaker lugs together.  That sort of problem will usually mean just a blown fuse.  Only a very poorly designed amp would not have protection from such a common accident as that one.

With tube amps, there would be no problem with a short of this type.  While people often talk about tube amps being prone to failure from a speaker wire being disconnected, that really only happens if the amps were being played very hard and the disconnection were for a long period of time.  Even then, I have never heard of an amp actually failing from this theoretically problematic condition.

It is a good practice when doing ANY sort of work connecting and disconnecting wires--speaker wires or interconnects--to have the amplifier turned off.  This prevents any sort of problems with shorts or loud pops coursing through the system.  

One other thing to ask, were you playing any music when you moved the cable?

If not, a short would only blow a fuse if you have DC on the amp outputs.  This might be worth checking before reconnecting your speakers.

I’m sure you new interconnects were not faulty but you could check with a volts meter to make sure signal wire is not crossed with return. If there was a problem or defect with interconnect it could caused amp to shut down.
 

I would think there would be more than one fuse for the amp other than just the one on the IEC inlet. Maybe one on each rail. I don’t know your amp so may not be the case. Good luck finding the problem.

I’ve been in your shoes, I crossed speaker cables on a McCormack rev a DNA 1and it blew the fuses on the rail. Not a good feeling, luckily got it up and running. Hang in there you will have it playing music again soon one way or another, YBA makes very nice musical gear.

Sorry,  thought you new cables were interconnects not speaker wire, should have read more thoroughly