I think for about 90% of people, these things work without any need for such complications. Most people have no need of an HDMI Detective.
That's a last resort option. If you need to buy one, you'll figure it out after a bunch of testing. I have several HTPCs, and only one of them needs the HDMI Detective Plus - the other two have no issues at all.
I am surprised that you expect a video card to sync with a monitor that is not turned on. My monitor is in standby when it is not fully turned on and the boot process causes it to fully power on(wake up) and then sync. I also have it set to wake up if the keyboard is used or if the mouse is moved. The settings for waking up are in the system BIOS and are not tied to the graphics card.
I hope this helps...
I have one HTPC that has the 450GTS, I can boot up with the LCD on standby, I have not tried it with power off.
Sony 40" LCD connected via HDMI.
PS I have had various other HTPC's with ATI card's that cannot do this.