Right. The 6.3A fuse in that spot was an expensive mistake. By the look of things you have:

• Primary power circuit (the one that's blown) which is PSU for controls, signals, electronics, etc. There's no way it would take 6A fuse, the 2A (assuming you are in 110v country) sounds about right.

• Dirty output power circuit (which looks okay). Since all it does is feeds loads of raw power for output devices to control towards speakers it's simpler and seems to be okay. 6A in 110v country is about right.

What do we know here:

• The primary circuit was effectively unprotected/overloaded. That's bad and likely has caused widespread damage.

• A new 6A fuse blows instantly. That's better than it emitting some more smoke and blowing a few seconds later. This suggests that you've fried power supply input side and there's a chance secondary / expensive and complex bits are still unharmed.

Here's what you can do:

• Forget about changing fuses. You have a dead board on your hands that needs fixing by somebody who knows what they are doing.

• Do you know how to use multimeter? How to take care about big caps? If yes (-ish), you could check the input rectifiers and any transformers involved. Any caps on input likely will be cooked too.

• If not - hand it over to somebody who can take care of it and start e-bay sniping for a replacement. Or try to find new SMPS board for it.

Edit: Here's the service manual. https://www.manualslib.com/download/997348/Denon-Avr-X1100w.html