A little confused on how to properly integrate my sub

Hi everyone! Im relatively young and inexperienced when it comes to the more complicated electronics side of audio. Right now for my computer desktop Im using a a pair of LS50s connected to a Musical Fidelity M3si integrated amplifier. I also have an REL T9i connected to the finding posts of the amp and use the High level input like REL dictates.

Ive decided that I really want to properly crossover my speakers and let the sub handle ONLY the low end. I decided to put my Musical Fidelity up for sale and have ordered an Outlaw RR2160 that has integrated bass management. I plan on using a standard unbalanced RCA cable from the Outlaw to the REL. The problem is REL makes this very difficult. Unlike another sub I have where there is a switch that lets you use a filter in the sub or amp, the REL provides no such option. They demand you use play your speakers full range. The knobs on the back of the sub are LO/HI Level (volume I think), Crossover (30hz to 120hz), and .1LFE level (im not plugging into that input anyway).

I assume what I need to do is set the crossover frequency on my Outlaw to 80hz (where I want it), and then plug the Outlaw into the REL through the low level input, then crank the crossover on the sub to 120hz. The sub should only be receiving the low frequencies anyway so by cranking the subs crossover up all the way I shouldn’t be attenuating any frequencies. Does this sound right to you guys? THANKS!
EDIT: After thinking about it, is there any reason not to use the LFE input and bypass the subs filtering? As I understand it, all LFE content is 120hz or below so the sub designers took that into account.