have i blown my amplifier?

With only remote connected to that amp, and your radio on, if you use the other amp's ground as a reference, you should get 12 volts on anything and everything in the Orion amp.  12 volts going in via the remote wire, the voltage goes everywhere looking for ground.  It can not find ground because the amp is not grounded.  12 volts should be everywhere.   The reason for the single 10 amp fuse was incase you accidentally touched pins 10 and 11 at the same time you would have turned the power supply transistors on wide open.  They would last about a half of a second in this state.  They would not blow 60 amps worth of fusing before they failed.

How are you at soldering?   Can you put your meter on ohms and verify that pin 8 and 12 are connected together.   Also check from 11 to 12.    Do you have an old IDE or Floppy ribbon cable that you can cut up to use one of the wires so we can make a jumper?

The ribbon cable on the laptop keyboard is not what you need for this task.  If you have to buy something, buy an IDE hard drive cable.  It will have 40 or 80 actual wires that you can use.   A 40 conductor harness will probably be a better choice for this job.  If pins 8  11 and 12 are all connected together, you need only 1 jumper.  If 11 and 12 are not connected together, (you will still need only one jumper) you will need to connect the jumper to both of those pins.   Cut the end off of the longest section of the ribbon cable and strip 1 of the 40 strands from the cable.  Strip each end of the cable back about 1/8 of an inch.  Heat up your iron and apply solder to both ends of the wire.  If 8 11 and 12 are all connected together via the circuit board, it will be safer to solder to pin 8, you can get to the end of the chip and should have no chance of bridging it to pin 7.  That would not be good.  8 is power and 7 is ground.  Heat up pin 8 and apply some solder to the pin.  Now that there is solder on each surface, place the jumper wire against pin 8 and heat both surfaces.  The wire will heat up, you need to be holding it back about 6 inches.  Once the solder melts on the wire and the pin, remove the heat and keep the wire in place as long as you can without burning your fingers.  Once the solder has cooled, gently tug on the wire to make sure it is connected good.   If 11 and 12 are not connected together, you will have to put the jumper on both of those pins.  Apply solder to both of those pins, place the jumper between the 2 pins, heat, melt and remove heat, tug on wire after it has cooled.   If 8 11 and 12 are common Just do 8.  It is much safer.

Remember only 1   10 amp fuse.    Plug up the power harness only.  No RCA no speaker terminals  just power.   Now briefly touch the other end of the jumper to the power block, notice if the light comes on,  if it does come on next time leave it on for a couple seconds.  If it remains on for a couple seconds and does not blow the fuse, connect the RCA and speaker connector and see if it plays.  Play it at low volume only, the 10 amp fuse will not go far.  If it plays at low volume we know that the power supply is OK, all we need to do now is figure out which transistor in the path between the remote terminal and the 494 is bad.  Let me know what you figure out.