That 80mm --> 120mm fan adapter won't work in this application. The Behringer amps are 2U tall which is 85mm tall. No way to get a 120mm tall fan into an 85mm tall amp. The only way to do this is to get some type of custom shroud which will allow you to mount the fan horizontally inside the case. I don't recall how much open space there is inside the amp case, but I can't imagine it would be enough room for that. It would be easier to create an external shroud that fits on the front panel if you insist on a 120mm fan. I just think it would be more trouble than it's worth for most people. Best bet is to go with a quieter 80mm fan. Maybe you can find a thicker 80mm fan that moves more air at lower RPMs. Again, I don't remember how much clearance there is in there.
Unfortunately, that Denon doesn't have 12V triggers since it doesn't have analog outputs it assumes you won't be using an external amp. You will need to get a smart power strip. In case you don't know what a smart power strip is it's one that shuts off one or more of the outlets on the strip when the device plugged into the master outlet is off. You will need one of those and a setup similar to mine. Plug the DC power supply to one of the controlled outlets. When the receiver turns on it will power on the DC power supply which will then trigger the relays to energize the outlets in the home made electrical box..
Just got the chance to pull my rack out to pull my homemade trigger setup out to take some pictures for you.
Here is the relay I use. You can use a single pole relay similar to a light switch where the bulb always has one neutral wire always connected then the switch disconnects the hot wire, but I prefer a double pole relay that disconnects both lines. This is added safety in case someone ever decides to take my "borrows" my invention and plugs it into an extension cord with the ground plug broken off and it doesn't have the plug blades key to prevent plugging it in reversed. Doing this will allow for a live hot wire in on the output side of my relay. Call me anal if you'd like, but to me it's just peace of mind. This also give you the ability to use the same device for 220V devices as it will disconnect both hot lines.
Anyhow, back to the picture. The two closest connectors in the relay are for the incoming 12VDC trigger.
Connect the positive and negative wires to these connectors. It doesn't matter which polarity goes to which connector. In my case, I connected it to a 1/8" mono jack. Now the four connectors in the back are for the 120V. They work in pairs. The left two are paired up and the right two are paired up. It doesn't matter which pair you use for the hot and neutral lines, but make sure you connect it to the correct side of the receptacle to maintain correct polarity. The ground doesn't go through the relay. Again, for safety purposes the ground wire is always connected.
Here's a shot of the 1/8" mono jack on the side of the box. I have one on each side for ease of placement.
Here are some photos of the 12VDC distribution box.
1/8" mono jacks.
Standard 12VDC input.
12VDC power supply.
1/8" stereo cable (mono cable will work also).
Photo of how everything is connected together.
Chart of how everything is connected.