I have the ADI-8 DS. I don't use the double speed rates (88.2/96) a whole lot though. The D/A side is more important to me than the A/D, which I don't use every day.
I like the unit quite well; sometimes I think the analog front-end could be better. I had the box open once; I forget exactly which opamp it was, but something generic and uninspiring. I would have liked to see them spend a few more bits there because the actual conversion seems very nice. I thought about modding that, but while I'm OK with SMT work, rework is a different issue . . . plus I need this box working in the rack, not sitting on my bench.
This replaced an old Alesis AI3 a few years ago; it's waaaay better than that, and better than the conversion in my HD24 (not XR version) too. I mean night and day with the AI3; that's the kind of comparison that makes one believe in the quality of conversion. How much better does it get? Well, there are lower noise units in the higher end, and I suspect if I did more 88.2/96 work, I'd see more of the shortcomings of the RME, provided I could hear that high . . . but the RME's behavior up to 20kHz seems well controlled.
I wish the box could be controlled via software as I don't like getting up to press a bunch of buttons to change rates and clocking and levels. But that's true of many things, I guess. I don't know how that could be implemented though; maybe for users of RME cards there could be some sort of secret handshake?
So anyway, the RME is going strong three years on; used a few hours daily.