Connecting Late 2006 MacPro with DVI port to HDTV

I went on monoprice and found a DVI-to-HDMI adapter and a standard HDMI cable to connect the computer to the TV. However, tech support said that there's no way to get the sound from the computer to the TV.

Which is correct since DVI doesn not pass audio.

I get the DVI-to-HDMI adapter + HDMI cable to connect the MacPro to the HDTV for video

I then connect the Optical Audio-Out from the MacPro into the Optical Audio-In on the DVD player/home theater-in-a-box

or

I can connect the audio out (headphone jack) from the Mac Pro into the Red/White Audio-In on the DVD player/home theater-in-a-box

Those will probably work but consider the following:

DVI & S/PDIF Digital Coax/Optical Toslink Audio to HDMI Converter

you can connect the DVI and optical out to that box and it will combine them into a HDMI connection to pass to the TV. Only limitiation is it's 1080i not 1080p. I use one of these boxes.

Yes, I think you got it all right, including the fact that only a single cable to the TV is necessary. And all the other cables can be found on monoprice as well.

I did it this way sort of by default due to (a) possible adapters at reasonable prices and (b) the requirements of having two active adapters on 5x70 cards when supporting three monitors.

One of my monitors is a 27" ACD and thus ties up one of my mini-dsiplayports (mDP). Second monitor is a VGA and third is the TV. So these need active adapters. Active mDP-to-HDMI were problematic. So I ended with a mDP-to-VGA adapter (considered active #1), and that box for the TV (considered active #2).

You apparently don't have three monitors to worry about so there more degrees of freedom. But using the digital optical for audio I think is still better than choosing the analog audio especially going to a home theater system.

There are some problems with connecting/disconnecting a monitor unless you do it while shut down of course. It will potentially affect your monitor organization. And if the system doesn't detect the monitor is not there then the system will think it still has the monitor which can get confusing if you happen to move the mouse on there!

Of course if you are using a 5x70 card you have the same active adapter considerations about having two active adapters. If you are not using those cards you may still need to investigate whether active adapters are required.

There's no way around that. But as for connecting/disconnecting a monitor you should look at SwitchResX. It uniquely allows you to deal with multiple video configurations. That's what I use to disable/enable my TV. And because it allows you to associate an applescript with each configuration you can switch the audio output as well. So with a menu in my menu bar, or a hot key I can enable/disable the TV and switch the audio between my computer speakers and the TV speakers.

The benefit is obviously no physical connecting/disconneting cables. Over the long term this also has the benefit that you won't physically wear out the connections.