OS v6.5 is fine for the KC, and is the latest OS for the Virus C series. The version/number doesn't relate to the later 'Ti OS'.
The Virus A originally released in 1997 went from v1.0 up to v2.8, the Virus B/Classic to v4.90 (build 050), and the Virus C/XL to v6.5. After the Ti family were released in 2005, the new "Ti OS" reverted its naming back to v1.0, wiping the slate clean for the Ti|1, Ti|2 and the Snow. The TI OS has since reached v5.1.3.0 since then.
Unfortunately I have not encountered the 'error' patch problem. I would either rattle off an email to Access:
http://www.virus.info/page/render/la...resources.html , or possibly reinstall the 6.5 OS for Virus C - which also includes the factory patches too.
How come you're replacing the LCD too?
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PS > And another thing! Will the Ti|3 have user customisable/importable wavetables?

A ribbon-controller or XY-Pad might be nice, too, please! Thanks!