panel enhancements are in theory relatiely simple, especially 2D panels. There is a very good piece of software around called FSPanelstudio (Fspanelstudio.com), and it is reasonably priced. With that editing panels is a breeze.
VC are a bit more difficult, because the information is embeded in the aircraft model. Sometimes your panel.cfg has got some entries starting with [Vcockpit0...]. These are the places where you place the instruments for the VC. The snag is, that there are no background bitmaps to aid the placement of the instruments. You in actual fact have to keep the dimensions of the gauges and replace them one by one, but with FSPanelstudio this process is also relatively easy.
Now, for the Dornier... I don't know what Marcel has done, the placement or changes of gauges in the 2D panel has an effect on the VC, which does not show any instruments at all, just the panel bitmaps.
That is the point, where I am battling. I'd like to "modify" my Dornier for peronal use, with GPS and other modern instruments.
AVsim has got a huge amount of freeware gauges, some of them very useful and others are just replacements for the default gauges. If you are looking at very good avionics, check out the payware Simflyer gauges or RealityXP. The latter are a bit more expensive, and I have no knowlege how they compare to the Simflyer avionics. I guess it is a personal choice and the size of the wallet.
Sorry Marcel for mentioning different manufactures
. I do not want to promote anything, just give my personal option.
Chris, I hope this helps.
If you need more information or help, pop me an email.