Using PS Elements 7, I had RAW 4.3. All of my Canon XSi files opened as 16 bit color in the RAW editor. If in fact I went into Elements itself, I could do little to nothing unless it converted to 8 bit.
I updated to RAW 5.5 and now those files open as 8 bit. Did I do something wrong or was this a change?
Did you verify at the bottom center of the ACR window that the image is set to open in 16bit? If that clickable text says 8bit, click on it and specify 16bit in the popup menu in the dialog that appears.
There is a setting at the bottom of the ACR window that sets the bit-depth coming out of ACR.
Check the "16-bit" box at the bottom of the Camera Raw dialog.