I used this reg hack previously to fix the Fantom synth issue with Sonar X3, but when I upgraded to Sonar Platinum earlier this week (and did a fresh install of everything, including my OS), the fantom synth problem returned. This time, the above registry hack did not fix the problem, and I figured out it was because Sonar Platinum uses a different directory structure in the Registry than previous versions of Sonar. To account for this, I altered the above hack to this:
 
 
[HKEY_CURRENT_USER\Software\Cakewalk Music Software\SONAR\Cakewalk VST X64\HardwareSupport]
[HKEY_CURRENT_USER\Software\Cakewalk Music Software\SONAR\Cakewalk VST X64\HardwareSupport\ARX]
"Port 1"="ARX (VS-700)"
"Port 2"="VS-700 ARX"
[HKEY_CURRENT_USER\Software\Cakewalk Music Software\SONAR\Cakewalk VST X64\HardwareSupport\ARX (2)]
"Port 1"="ARX (2-VS-700)"
"Port 2"="VS-700 (2) ARX"
[HKEY_CURRENT_USER\Software\Cakewalk Music Software\SONAR\Cakewalk VST X64\HardwareSupport\Fantom VS]
"Port 1"="FANTOM VS (VS-700)"
"Port 2"="VS-700 FANTOM VS"
[HKEY_CURRENT_USER\Software\Cakewalk Music Software\SONAR\Cakewalk VST X64\HardwareSupport\Fantom VS (2)]
"Port 1"="FANTOM VS (2-VS-700)"
"Port 2"="VS-700 (2) FANTOM VS"
 
Saved it as a reg file, and migrated it into my registry. And lo! The Fantom synth now works. A minor tweak, and not hard to figure out, but I figured I'd save someone who isn't that familiar with the registry a few hours of frustration by posting it here.
 
The usual disclaimers apply: muck around in the registry at your own risk, and while this hack variation worked for me, it may not work for everyone. So, you take your chances. But I figured it might help someone!
 
I'm using Sonar Platinum, Windows 7 Home Premium 64 bit, and V-Studio 700.
 
Good luck, folks.