As far as not using TH2G and using 2 cards, I paid over $300 for the darn thing, and sure cannot afford a second card right now. Besides, I got the TH2G for that added realism and peripheral view.
Like you and CHriz6662 I bought TH2GO mainly for FSX.
FSX is heavily promoted on the Matrox site so I just assumed they worked perfectly together. Only after encountering this problem and returning to the matrox site did I notice that none of their
FSX screenshots have a 2D cockpit. I share your disappointment. I feel mislead.
I'm not optimistic that there is a solution, nor will there be. Do you know that Microsoft has stopped all development on Flight Simulator, disbanding the development team?
I suspect, it is only speculation, the problem has to do with the separateness of the panels. TH2G can successfully stretch the main scene but fails to adjust the panels properly. Perhaps getting a panel editor out and manually adjusting the panels might work? Even if that worked I'm not sure it would fix the frame rate drop and wild cursor issues.
If you can endure the workaround I mentioned, having a 2D cockpit and scene on the centre window with panels undocked to the side screens, then you don't need a second graphics card for this. Just start up via TH2G as normal and resize the main window to the centre screen. (I haven't tested this).
Although disappointed with this mere workaround I console myself with the fact that a 22" widescreen is far superior to my previous 17" narrowscreen. Plus I can move the panels (throttles, GPS, ...) out of the way. And 50,000 people die each day from poverty. Well that's not "consoling" but at the very least I don't feel too hard done by.
I mentioned the second graphics card as my default mode is "Independent Mode", which does require a second card, which I use for development/office work. I switch from Independent mode to "TH2GO/Stretched" mode when I want to game. If you exclusively use "TH2GO/Stretched" mode then you don't need the second card.
Independent mode, with Ultramon, allows me to place the start menu on the centre screen and have each of the monitors with their own task bar, which helps to show where each minimized window dwells.
By the way, if you work (as opposed to gaming) in either mode I highly recommend
gridmove. Gridmove does much more than Matrox PowerDesk (Desktop divider) or NVIDIA Desktop Manager (User Interface > gridlines). I have created some grids for three screens, in either mode, which I hope to get around posting at some point.