Extending 2007 iMac display to HD projector?

I have a 2007 iMac and an Epson 730HD projector. I want to dedicate this iMac to playing media on the projector but I'm having problems with extending my display.

I'm using a Mini-DVI to HDMI adapter and connecting to the projector using an HDMI cable. The computer is detecting the projector, but the projector is saying there's no signal. I've tried playing with all of the resolution settings–thinking that maybe the projector just didn't like the resolution that the computer was sending–as I've had this problem before with other displays and setting the resolution to "Best for display" usually did the trick. The projector has a native resolution of 1280 x 720, I've tried every scaled resolution while extending the display and while mirroring. No luck.

My MiniDVI to VGA adapter works, so this appears to be only an HD problem.

Is there anything I haven't tried? Or is my iMac just too old for this projector?

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^{Screen captures of available scaled resolution settings:}

^{My Mac (24" Intel iMac, 2007):}