Crossovers and Low Pass Filters

I have been using low level RCA connection from my integrated to hook up my subs. My integrated has both hi and low pass filters that can be set by a crossover point. 

How should I look at this and how should I go about setting proper crossover? I thought that because I was using the low pass filter on the integrated I was actually setting the crossover for the sub and therefore I have been turning the crossover setting on the subs all the way up. This doesn't sound good. 

My subs are REL t7x (pair) and I have had little success using the Neutrik hi level connection therefore RCA low level.