Cant afford a new one. Love this one want to fix, want to learn.

So I’m learning a lot here, but needing help and guidance.
Its a onkyo tx sr 507
can post photos Of PCB if need be.
I only us it for 3.1 FL FR C (Lfe SUB)
There is a nice schematic here is a link if im allowed, if not look for "onkyo_tx-sr507_sm"

I got a bad AVR.
Have learned it has a bad channel.
It seems all channel are made up of the same electrical components.

It blowed fusses, not the main but the other two, that work the speakers i think. I replaced and they went bad again. I dont have sound but video still works. even with fusses bad, or out.

also there was smoke, think it was from glass fuses going out, is this normal or did something else cause this.

AT this point i have it torn down. waiting to solder/ test.

Help explain AVR amp circuit:
Anyone care to explain how this circuit works? Like I know there are different parts to it, with specific names. Like there are 12 transistors but I know they do different things, but what I don’t know, also I don’t know their names. The other parts in the circuit likes caps, etc… I have question about below.

Help explaining Transistors:
Why are some transistors in different packages? I know the NPN, PNP thig but some are round like caps, others have screw hole with thermal paste on heat sink, and other have whole look like they should be on heat sink but not.
Also I in my reading I see people say if your speaker transistor are shorted (assuming the big transistor that come in pairs on heat sink) to check the collectors, and emitters. All the other transistors ( all transistors) have an emitter and a collector. Why are they calling them by their legs? ( assuming its has to do with the specific area of the circuits)

MY Plan:
To pull good components from the channels I don’t use. (the back surround) to fix my Front Left channel. If that’s all that’s went bad. Then order parts to put in to back surround, that way if the sound is off it wont be as noticeable as when I do get back speakers they are not used as much.
This good logic?

I have learned a great deal about transistor in a short time
Seems I have a pair of shorted transistors that drive my front left speaker. (tested in circuit)
Based of schematic it seems I need to remove them to check the rest of the circuit as I got other transistor testing bad in the front left circuit. So it seems if one items is bad, it could make them all look bad. Based on how they are wired together ( I could be wrong )
Is this right? Or can I check these in circuit or do I just start De-soldering parts one at a time and check that part if good put back move on to next.

Gear I have:
I have a uni-t ut61 DMM, I have random electrical components from spark fun inventor kit, old PSU can turn in to bench top psu.

I need help checking the parts. He is what the circuit is made of:

Resistors :
Look for visual burned marks or cracks.
check to make sure it matches marking and the schematic using dmm
How much ohms do I over look due to % rating of resistor. What about the ohms of my DMM and test leads. I know this stuff will mess with readings.
This have to be out the circuit to test right?
Noble resistor
Aka fire proof? Aka emitter resistor? Aka sandstone resistor?
What is its name, its big, white has two resistors in one, they share the middle leg.
How do I check it visual, what about with my gear?

Look for blown apart, leaking, or visual damage.
Can this be test in circuit?
Is there a way to test this with equipment I got? If not is there some cheap knockoff from ebay I can buy to test them?

Visual damge what am I looking for?
I know to test for shorts between legs.
How do I test this in with dmm in diode mode? How does this work?
Any other way to test if these test or not the best? I think there is something about apply voltage to a leg and see if it switches??

Diodes :
Visual damage what am I looking for?
My dmm has a test mode, I look to make sure this thing is a one way road right?
Does it have to be out of circuit or can it be in circuit?
Any other info?

There is a variable resistor (rheostat) I think.
I think its used to set something to the right number so that all speakers are in synchronous or sound the same or have same volume.
I know it need set after you change components. Would I need to set this if I use the exact same components to fix the channel aka rob them from back surrounds?
How do I check this part for damage what do I look for with tools and visually?

Thanks for reading, for your time, and hopefully your help.