Why did my amp just crash and burn ?

Hopefully it is just a blown fuse.

However the hissing sound may be a symptom of a larger problem.  It could also be just a coincidence it coincided with the cable swap.

I can elaborate more, if a fuse swap doesn't fix the problem.

@ozzy62 

Looking at the YBA YA201 manual :

Fuse - 6 A ( versions 110v and 117v)

ou 3.15 A (versions 230v)

I will try and open the small drawer compartment above the power cord later today.

Btw, just spoke with the tech dept at AQ, ITO, applying the left cable to the right channel and vice versa should not have any attendant issues. Sound will just be transposed in the process. They believe it might just have been a power spike or surge last night, which is possible. As for the cables, the chances they were damaged would be quite low. Although , as we are finding anything is possible with audio system setup.

@blackdoghifi I would value your advice if  the fuse does not fix the problem. 

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.