Campaign Availability and Retroactive Engine Improvements

I was wondering if anyone would be able to clear a few questions up for me, relating to the various campaigns available in Galactic Civilizations II. For starters, as I understand it, each of the GalCiv II games, the original Dread Lords, Dark Avatar, and Twilight of Arnor, have their own distinct campaigns. Additionally, in each successive expansion pack, many improvements have been made to the original GalCiv II ranging from AI, to graphics, to tech trees, and so on. What has confused me, then, is exactly what the upshot (in relation to the games that came before) is to these additions that have been made with each expansion.

If I were to open up the original game and start playing its campaign, having installed either one or both of the expansions, would I see any of the improvements that were added by these later releases? I have also seen mention, in a number of threads, of the fact that it is possible to open up the original campaign in at least Dark Avatar - how would that affect it? Would the original campaign then benefit from Dark Avatar's newer advancements?

Additionally, some have mentioned that it is NOT possible to open up the original campaign in TA, though it may be possible with the upcoming 2.0 upgrade - is that the case? And if so, if the capability IS added at some point in the future, would the original campaign benefit from everything that was added in both DA and TA?

Expanding on that, can the DA campaign be opened in TA, or does it suffer from the same limitation as the original campaign? And, once again, if it either can now or will be possible in the future, would the DA have all of the TA upgrades?

Thanks for any help that can be provided - all these different versions and varying levels of intercompatability (both content wise and technology wise) have gotten me quite confused