Well, basically, you have two choices.
1: Install a Windows XP partition to boot to when you need to use Hypersonic 2 (and forego using anything that requires Vista or newer), or
2: Give up on Hypersonic 2 and replace with Halion Sonic, M1, Purity, or other workstation VSTs.
That's just how it goes. Sorry. If it's any consolation, Hypersonic 2 wasn't really all that amazing anyway. It was very efficient (which isn't quite as important if you bought a new, modern computer), and had a decent package of sounds that were quick to browse through.
For what it's worth, I'm waiting around with my fingers crossed hoping that Korg will update M1 and bring it into the world of 64-bit.