I've found it. I had it in a location not being scanned as it is 32 bit. I don't use any custom plugin layouts.
After moving it to the proper folder, It shows up bit-bridged (as expected), but I get a message saying that it is "not suitable for this host and will be bypassed". Same message in Sonar 8.5, X2 and X3. All installed with their respective updates.
I'm reluctant to do a reinstallation of X2 as I'm worried that it may overwrite some shared files/utilities (for X3) with older versions and mean I might need to reinstall 3 and it's running fine at the moment.
There's nothing in the VC64 I haven't got replacements for but I like it as it's a complete "make it sweet" package.