OK. I think I know what is going on with my setup.
Forgive me if this is technically inaccurate but I am working backwards from the behavior rather than theory which I have no clue about.
Basically I think all the oddities are happening on my setup due to one basic fact - 1080p and 1920x1080 are not the same type of signal.
My TEAC LCD TV works perfectly happily if I send it a standard DVI computer signal - anything up to 1920x1080 works fine from any number of computers.
Now, with the GA-MA78GM-S2H being specifically designed for HTPCs, it gets all fancy and sends a different type of signal... a 1080p signal if it detects a LCD TV and a 1920x1080 if it detects a monitor such a my Dell 2405.
I am at a bit of a dead-end testing wise now as I have no way of testing whether my LCDTV is faulty and is not handling the signal correctly or if its the motherboard... if I had a set-top box or some other comsumer electronic device that output over HDMI then I could... tomorrow I hope to test the box on my friends LCD TV.
So it is down to one of three things:
1. Motherboard design/release problem - could be drivers/BIOS etc
2. Faulty Motherboard
3. Faulty LCD TV
If anyone knows how I could go about tricking the MB into sending a computer signal rather than a HDTV signal then I think it would work perfectly...
Any thoughts or comments?