Hi there,
just a small clarification of what that “compatibility chart” really means. Cubase 6.0 and Cubase 6.5 haven’t been tested by our QA department on Windows 8.1 and Mac OS X 10.9. This doesn’t mean that they won’t work, it only means that we officially offer no technical support for this installation. It is very possible that it does work, it is even possible that it works better than in other constellations, but it is also possible that it won’t work at all. The thing is that we don’t know, because we haven’t tested it. Cubase 6 was discontinued two years ago and the last update was released last year. Cubase 6.5 was discontinued last year and its latest update was released earlier this year. The official maintenance for these programs is officially closed and no compatibility patches will be released for new Operating Systems, which is the main reason why this wasn’t tested nor will it be supported. If you want to work with Cubase 6.x on the new OS, it is up to you and it will be on your own risk, which still doesn’t mean that it won’t work.
To much bla bla bla from my side, but I hope it clears things up a bit.
All the best