I would start with -0 for highs just to see how it sounds.
You should tune your sub amp to what music you listen to, if you listen to alot of decaf, bigpimpin, etc, then set subs to -5 or -0 to be safe, if you listen to alot of "punchy" rock with loud kick drums then set amp at -10, & if you listen to songs that don't have very much bass at all like oldies then set amp @ -15. It's all relative to what music you listen to.