It was here on my old XP drive:
 
D:\Program Files\Cakewalk\Shared Plugins\StudioVerb2.dll

Well, I've figured it out... sort of...
 
It turns out that the plug is in the advanced installs for X2, X1, and 8.5 (the oldest version I have), under the very descriptive name "Reverb"
 
But here's the thing... even if you select the option to install it during a 64-bit install, the corresponding files will not be installed. They will only be put on the system if you do a completely 32-bit installation.
 
But even then, running a 32-bit installation of X2 with the "Reverb" option checked did not install the necessary 'studioverb2.dll' file. It only installed the StudioVerb 2 help and 'DShowProxy.dll' files. I had to go back to X1's installer to get 'studioverb2.dll' in there.
 
Well step one was simply finding the plug. Step two was seeing if it would function. Left as it was installed, after a VST reset/scan, it wouldn't even appear in X3. Long story short, the closest I came to getting it to work was by using DXShell to convert the plug into a VST, placing the resultant .dll into a Cakewalk-scanned folder, with another reset/scan. That got StudioVerb 2 to appear in SONAR, and look as if it was going to work, only for me to be met with this error message: "This Plugin is only licensed to be used in Cakewalk Project 5. An unrestricted version can be purchased from www.dspfx.com"
 
And with that, after trying every possible solution I could find, I've finally taken the hint -- this plugin just isn't going to work in 64-bit SONAR.
 
I just find it strange that this particular effect was not modified to work in 64-bit, when all of its sister-plugs (AliasFactor, Tempo Delay, etc.) were. Was the effect just not that popular? Did someone simply miss it in development? I'm very curious. (If any Bakers happen to float by this thread who may be in-the-know, please chime in!)
 
But whatever the case, that means that this list that I originally cited is arguably erroneous, in that there should be a "(32-bit Only)" note beside "StudioVerb 2", instead of the indirect implication that it is 64-bit compatible. The same goes for the "Reverb" listing in the installers, but I know that those are all said and done.
 
So if anyone else is wondering if they can get StudioVerb 2 to work in 64-bit SONAR, my exhaustive advice would be this: spare yourself the time and trouble, and focus on enjoying all of the plugins that do work.
 
 
Side note: During my hunt for StudioVerb 2, I noticed a few other entries on the aforementioned list that truly seem to be nowhere to be found, either in installation or within the program: "Chorus", "Delay", and "Flanger". Interestingly, their CFX mono counterparts are present.

If I remember right the half-rack units were originally in P5 as said above.  They were based on the DXI but VST and got introduced into SONAR even before P5 died (this is all hazy since it has been a few years).  I've still got them on my computer, but that has X1 and later on it.  Plus some older Cake effects I originally loaded.
 
I wonder if I can find the disks if I do a clean install to Win10?
 
@

I know this is a year old but...
 
On my 64 bit Windows 7 system Studioverb2 works fine in 32 bit Sonar but will not work at all in 64 bit. Same with my new 64 bit Windows 10 system.
 
Sonar Platinum does not even have Studioverb2 so of course it will not be installed. To get it I had to do a FULL install of X1 (X2 or 3 will also work).
 
At first I tried to install it by running the 32 bit X1 install and selecting only the FX I wanted with no program files (I did not want X1 on this system). Some of them installed but Studioverb would not. Before giving up I did a full install and it showed up... and it works in 32 bit Platinum too.
 
This is why I keep both 32 & 64 versions installed. Those tracks that need Studioverb (or any other 64 bit banned plugin) can be opened in 32 bit Sonar, processed, frozen, and exported back into 64 bit Sonar.