I see that you installed both sound sets, but which one do you use? In the Playback Devices you find a list of active devices. You probably activated Vienna Ensemble. In the right column you see the sound set, that is loaded. If you want to use the PLUS matrices, you will have to load the VE Special Edition PLUS sound set.
Andi

If you want to use Special Edition matrices (without the +), you will also need the normal Special Edition sound set. It can't be bad having both of them installed.

I guess you copied the sound sets to the wrong folder. Please copy them to the following location:
Windows XP: Documents and Settings\your username\Application Data\Sibelius Software\Sibelius 5\Sounds
Windows Vista: Users\your username\AppData\Roaming\Sibelius Software\Sibelius 5\Sounds
Mac OS X: Users/your username/Library/Application Support/Sibelius Software/Sibelius 5/Sounds

You may have to create the "Sounds" folder if it’s not there.

Sibelius needs to be restarted after that.

Andi

Which Sibelius version do you use?
Sibelius 5.1 only finds sound sets for Sibelius 5.1.
Sibelius 5.2 and 5.2.5 only find sound sets for Sibelius 5.2.

Maybe you downloaded the wrong versions of the sound sets.

Can you please tell me, which Operating system you are working on and write down the exact path where you copied which sound sets (or post a screenshot)?

The path is correct. Which file(s) did you copy there?
In your case the following two files should be in there:
VE Special Edition (Sib 5.2).xml
VE Special Edition PLUS.xml

When these two files are in the folder and you activate Vienna Ensemble in Sibelius, you should have the possibility to choose "VE Special Edition" or "VE Special Edition PLUS" (amongst others) as sound set.

Andi

Sometimes simple mistakes can take time ... [;)]

I'm glad, we figured it nout now.

Andi