spot on IMHOAs you've probably realised by now an open question like this invites all the pro-ATC users to pile in blaming everything else but the speakers! I would strongly recommend you believe and trust your ears. You've made valid comparisons between ATC's and R50's with the same sources. I would suggest as some others have the ATC's have a frequency response which may not suit your preference and room. If you had asked ATC themselves they'll tell you to treat the room first. However this glosses over the fact that the speakers are designed to have a flat frequency response in a professional recording studio which means in the average room you get a treble tilted response. On very good recordings having not much treble content IME this produces superb results with excellent sound staging, dynamics and detail, but with average recordings compression and other artefacts become irritating because they are reproduced at a higher level than intended.
You have already got some helpful advice on this thread if you filter out the noise. I'd suggest you try and get a dealer demo of ATC versus Tannoy Kensington GR or similar to confirm the suspicion that ATC's are not your cup of tea, and check Acoustic Energy Corinium speakers which just might be! Also the "soundstage collapsing" problem isn't what I would associate with ATC so you might also want to try out the problem recordings with a better source. It could be the recording is actually poor and the R50's mask the issue while the ATC's shine a massive spotlight on it. But speakers first!