Photoshop :: 10-bit Color Works In LR4 Develop Module But Not In CS6

My setup is a ATI FirePro v4900 connected to two monitors: an Eizo CG276 and an old second monitor. I would like to get the Eizo to display 10-bit colors in PS CS6 under a 64-bit Windows 7.
 
After setting everything up, I am at a point where Lightroom 4.4 displays the notorious ramp.psd file (see below) without banding in the develop module, hence I assume 10-bit is working there. In Photoshop, however, I had no success so far to get 10-bit to work.
 
Here's what I've done so far:
 
I set everything up as described here [URL] ...........
 
Summed up, I did:
1) enable 10-bit mode in ATI driver and rebooted -> checked and this is still enabled after reboot
2) open PS CS6 and enable "advanced" drawing mode and 30-bit display in the "performance" options and rebooted  -> checked and this is still enabled after reboot
 
I verified that the monitor runs in 10-bit mode using Monitor Asset Manager 2.6 [URL]. It states that Color bit depth is "10 bits per primary color", which is what I want.
 
Then I tried to open the ATI 10-bit test file ramp.psd [URL]. In Photoshop it shows banding. As I've read that Lightroom 4's develop module uses 10-bit, I opened the file there and it had no banding.
 
The only troubleshooting I could find for 10-bit colors in PS was this post [URL] ... however I do not have desaturation set in the color preferences of PS, hence it does not apply to my problem.