If you can open even one PSD file in ACR, you should be here answering questions - not asking them.
I am also confused by your Photoshop version numbers. Do you mean CS5.5 and CS6 There was no CS5.5, although there was a Creative Suite CS5.5 which obviously contained Photoshop. Or are you talking about early versions of Photoshop? PS5.5 (Strange Cargo) was released in February 1999 and PS6 (Venus in Furs) in September 2000, but Camera RAW support didn't arrive till version 7.0.1 in August 2002.
ACR can open RAW files, plus JPGs and TIFFs, but not PSD files.
You're correct; I used the Creative Suite 5.5, which contained Ps, and now I use the Mastercollection 6, which contains almost everything .
In Photoshop I can open PSD-files: File>open as>choose Raw file.
Well I never!!! All these years and I didn't know that! I just tried it wit a layered PSD file, and, of course, it only shows one layer. Unfortunately, having set that preference, it then wants to open all PSD files in ACR.
[EDIT] Sorry, I have no idea how or if you can sync multiple psd files.
But how do you set that preference?
When I "open as...", I can choose in a dialogue-window in what program it opens, but I don't know how you make this a preference.
I've tried that, in Bridge, but there is no option/ preference to open the psd-file in Raw.
That was possible in Ps from my Creative Suite in 5.5, now I have to make an extra step: first open Ps, then "open as".
But as I asked; how can I use that option for several files simultaniously?