Not that this helps the OP but ...
The discussion never resolved the question raised by phoenixengr: why is there an improvement in sound when using a flywheel? Seems to me a likely cause is motor isolation. The flywheel adds a buffer against vibrations. Those VPI motors are noisy in my experience. I found that moving to a teres verus motor on my Aries 1 - essentially making it an idler wheel tt - improved the sound dramatically. So much so that I can't see ever going back to a belt drive.
The VPI Rim Drive had similar strong reviews but they seem to have mothballed it.
The discussion never resolved the question raised by phoenixengr: why is there an improvement in sound when using a flywheel? Seems to me a likely cause is motor isolation. The flywheel adds a buffer against vibrations. Those VPI motors are noisy in my experience. I found that moving to a teres verus motor on my Aries 1 - essentially making it an idler wheel tt - improved the sound dramatically. So much so that I can't see ever going back to a belt drive.
The VPI Rim Drive had similar strong reviews but they seem to have mothballed it.