I've been entertaining the idea of running my subs on an aux but not sure how I want to set the crossover point between the subs and the mains. Right now I run my SRX715s in passive mode and crossover the subs at 140Hz with a 24db LW slope and no overlap. I know some people don't like to have any overlap when crossing over between different bands but I'm thinking that if I run the SRXs as full range mains with a low cutoff around 60-70Hz, I would then want to set the low pass on the subs around 120-130Hz to get a little more low mid (chest thump) out of the system. Has anyone tried this?
The "best" sound you can get is from a single source, referred to as a point source. Once you introduce a second delivery of the sound from another source (speaker, strong reflection), the two sounds interact with both constructive and destructive interference. This is often expressed by the term "comb filtering".
In attempting to get more "thump" out of your system by having multiple drivers delivering sound within the same range, you are also going to experience the problems associated with multiple-source delivery interference.
Learn what comprises the "thump" you want and give it to your speakers to reproduce. If you simply need more volume, get louder speakers.