Many of Denon devices are implemented as "Generic Serial Device" which has a very powerfull interface, but for small things like yours there is a simplified syntax.
Take a look for example at Denon DVD-A11 (just add it as a device, got Wizard->Devices->Generic Serial Devices" and click on "Ruby source Code", you can delete it later, after you see how it's done there).
You'll see on ON command something like
<$"PWON\r"$>
Which practically means send that string.
In your case you can write something like
<$"\xFE\x03\xC3\x75"$>
Hope this helps.