Hi Holly,
Uh Oh, You've gone through my suggestions pretty fast.

- Your speaker connections are good if the system plays normal
until you connect the trigger wire.
This tells me it's something in the wire itself, the trigger output of the Denon, or the input of the Rotel.
This narrows down....well....all the easy stuff.
The only ones left are the trigger cable and voltage.
- Trigger cable: Does your Denon or Rotel
manual (not a Google search) specify a "particular" type of cable be used? You may have a recommended trigger cable, but you may have one of those unusual situations where you are 0.01% of the population and need a "XYZ" cable instead of the "ABC" cable that is readily available and used by the vast majority of the populous. Just maybe. You know how these things can be. No solution is always 100% accurate. There's
always an exception for one reason or another.
- Voltage: Do you have a meter that measures voltage? If not you could buy a cheapy for $10 at Walmart. The possibility remains I'm sending you on a wild goose chase and voltage isn't an issue, but........it could be. You never know until you rule it out. If nothing else, you'll have a voltmeter to check 'other stuff' in the future.
When you say,
"how would I use a voltage meter to find out what voltage the Denon is sending from the trigger output?"I'm not sure how much information I need to give here. Do you mean how do you physically
USE a voltmeter, and how do you connect it to the output of the Denon to test the output voltage?
I can explain, and walk you through it Holly, but it'll take a bit of explanation on my part. I want to make sure where we're at before I type a book, only to find out I've not typed anything you didn't know already.
Where are we regarding your knowledge of voltmeters and testing voltage? On a scale of one to ten, as 'one' being, "you've never seen a voltmeter in your life".......?
The quick answer to your question would be:
#1 Stick the trigger cable in the Denon
#2 Use alligator clips to hold the meters positive and negative leads to the other end of the trigger wire. (in
this case, polarity does
not matter.)
#3 Turn on the Denon as you normally would, keeping an eye on the voltmeters screen.
#4 Record the reading.
What I'm not sure about (but assume), is the trigger signal is just that. A trigger. Like a gun. It's sends a quick "zap" of a signal, just enough to wake up the piece of equipment downstream. OR, is it a longer, slower build up, stabilization, and drop off of voltage. Nice easy and slow. I'm not sure. But either way, keep a close eye on the meter, as the signal might be a very quick (milliseconds?) 'snap' of signal.
Again, if I were the person doing the testing in this situation, I might prefer to have an analog voltmeter as opposed to a digital one. My digital meter isn't quick enough to see 'snap' changes. An analog jobby would have a sweep needle you'd see go from the left side of the spectrum - full right - and back to left in a split second.
So, again Holly, do you have a meter of any sort?
Do you have a Radio Shack part number for the cable? Seeing it would help me know what we're dealing with.
With the exception of the actualy testing, I'd avoid playing too much with the trigger wire installed. It sounds like your Rotel is getting a wee bit pissed with the situation. I wouldn't press my luck playing with it. Only for testing purposes only. Know what I mean?
I'll do some digging for you, but I work tomorrow (Saturday) and have prior engagements Saturday evening and Sunday morning. If my reply time is a day or so, I'll be back, don't worry.
Bob