Nobody answered until now, so I'll give an update myself:
My current solution is to STOP BUYING DRM-med epub books (=.acsm) because you ONLY need Adobe Digital Editions for these files (for others you could use Calibre, which works great). If there are no unprotected books available for sale, then I buy them at Amazon. The Kindle application reader works fine under Linux (via Wine) and I use Epubor (not free, but it really works very nice and for me is worth the money) to get rid of the protection and to have it freely available in Calibre and to be able to put it nicely on my eraeder (Kobo Aura).
I have to say that it annoys me ENORMOUSLY that Adobe doesn't come up with a good solution for Linux-users.
To completely turn my back on epub .acsm files that needs to be opened with ADE first, is -at this moment- for me the best solution. (I tried Virtual Box this evening, but with no success yet, when I want to create a VM, it keeps coming with "This parameter must be a string or Unicode object" I'm a bit tired of trying things to get something to work so I didn't put much effort in this to solve it, yet. If somebody knows how this problem can be solved, I would like to hear it.)
They can't even get half the stuff working on Windows, why would they waste time working on solutions for 0.5% of their customer base when 99.5% use a dominate OS? It's Linux, surely you can work up a hack to fix it, isn't that why you're using it instead of Windows?
Just a note: you can install the .net stuff into your WINEPREFIX with winetricks.
It still won't work, but you can do it.
Personally, I think Adobe should just release an API so everyone can hook into the content network and authenticate and download DRM-encumbered digital products. Then they wouldn't need to keep developing this lame-duck reader program which most people use ONLY for accessing the content network. If Adobe really and truly feel the [awful, horrible, unmanageable] ADE experience is the best available [every tried Calibre? So much nicer.] then they should either actively develop it and make it work everywhere, including Linux, or release the source so other people can.