All you need to ask yourself is if RGB is important to you... and your decision is made. Personally, I'd go with the Z623s. My speakers don't need lights. But more importantly, I get the feeling that the Z623 system is going to be more, for lack of a better word, generic. The G560 is a gamer setup, so they are going to play with the frequency response and try to "tune" them for gaming. I feel like the Z623 are going to have a more flat frequency balance. That will make it easier for you to tune the equalizer to your own tastes. However, the G560 probably has better actual speakers.
As for the feature set... DTS:X is fantastic... when it is supported and works. The G560 is also going to need software to drive the lighting and sound...