Fl Studio 6 now installs flawless (except an "1400 error cannot access File List", but u can ignore it as it will work flawless anyways) in CX 7.0.0 and all of the interfaces work. Using is almost without interruption possible.
The only things that could be stressing are the Slicer, Soundfont, Directwave and some soundproccessing effects.
Piano rolls sometimes doesnt accept input. This can be fixed by reopening the pianoroll window.
Another problem could be the high latency. Either try to lower it to the cpu max or install WINEASIO, this will give u a fully implemented Asio Driver. If you cant get it to run under CX try it under Wine first and see how it works. (Wineasio will send it sound over Jackd, so jackd will be required!)
Get Wine-Asio here: http://sourceforge.net/projects/wineasio/
For 64bit users it might not work, instead use this version: http://people.jacklab.net/drumfix/wineasio-x.tgz