The infamous RME vs. Apogee david and goliath review (readable still on the RME site) is based on rigorous testing of various specs. The author of the review concludes (he doesn't say whether or not he actually listened) that both boxes are of such a quality as to have no sound of their own, which I imagine would be disputed pretty heavily hereabouts. Nothing is that transparent.
For the money RME is the clear choice. I've heard of one guy replacing the lesser opamps in the RME with Burr-Browns and loving the results. I don't know if I have the guts to do that to mine.
I am happy to have the RME and it serves me well and sounds as good as I can make it, definitely the limiting factor is elsewhere, probably the "engineer".
It sounds crystal clear and very dimensional, especially at 96khz. I'm pleased. I didn't know digital got this good.
Haven't done a direct comparison with the others you mention.
1/8" inputs? That is screwy. The ADI-8 DS has TRS (balanced or unbalanced OK) 1/4" ins and outs, TDIF, and ADAT lightpipe.
I'm real curious to get a hold of something really trick and see how much it improves things.