Well, I did not install 32-bit Dimension Pro, so I do not at the moment see that either, BUT I did install a 32-bit Sonar, and all of its included plugins and such, so Rapture does show up.
The 32-bit Rapture sounds are the exact same as the 64-bit sounds, and the same would be true for Dimension Pro. I do not believe any sounds are above 24-bits, so I think whether or not you are previewing in 32-bit Dim Pro or 64-bit Dim Pro, or whatever synth you want, I would imagine this Free Piano app would still fit the bill very well.
I am actually going to go ahead and install a 32-bit Dim Pro, as i REALLY like this Free Piano for browsing myself - this is of course all your fault, and I thank you for it. :)
As a matter of fact, I just bought the Arturia V Collection, and while there are 64-bit dll's for inclusion in 64-bit Sonar, stand-alone versions of individual synths, like their amazingly good Modular V are only present in 32-bit form. I believe that is because the sounds sound the same, and they just did not bother with creating a 64-bit app when it was not needed. It is only a 64-bit need to run without bridging in 64-bit Sonar.
So, I would suggest you just go ahead and install the 32-bit Dim Pro and then you can happily cruise the presets using the Free Piano.
I did not happen to find any 64-bit virtual keyboards, and to be honest, because the 32-bit one works well for me, I will likely not even bother to look for any.
Bob Bone