The only Voyetra Midi Orchestra Plus software I can know was written for Windows 3.1 and Windows 95. Thus there are several reasons for it to be incompatible with Windows 8. First, it was a 16-bit software; the most common Windows 8 installs use a 64-bit OS. This means that the OS has undergone a number of major changes. The installers are completely different (format/way of talking to the OS). The DLLs that communicate between the software and the OS have also changed. The drivers for MIDI devices will be totally different in the modern OS.
The documentation for Voyetra Midi Orchestra is available here: http://www.turtlebeach.com/support/files/241/
. It is a discontinued product and no one at the company that owns it will be writing a new version of the code for Windows 8. I'm not sure this software will work in Windows 7 32-bit. You might be able to use the software in a compatibility mode from a virtual version of XP. For Windows 7 Pro, Virtual PC and the XP mode package are available as free downloads and can be used if your hardware allows. Windows 8 Pro has Hyper-V but requires a licensed version of any Windows OS that you want to use. For non-pro versions of Windows software, you would need to buy a Pro upgrade. The alternative is to obtain another Virtual machine software (VMWare, for example) and a licensed copy of XP or an older version of Windows. (OEM Windows 7 Pro licenses are still available from many computer hardware vendors.)
I hope this helps.
(Many 32-bit device drivers don't work under Windows 8; older software that didn't run under Windows 7 have similar problems.)