I can echo others in stating that integrating a sub or subs can be a big challenge. I’ve fought many rooms and many single sub setups over the years trying to get things to sound right.
My advice is to keep trying since that sub you have seems to be a very nice piece and should add quite a bit of enjoyment. Move things, change settings, etc. as you have been doing until your ears tell you it’s right.
I’m a firm believer in a dedicated outboard crossover too where you can just assign low frequencies to the sub (low pass filter) and roll off the low end to your main speakers (via high pass filters). As stated a million times on these boards, getting those low frequencies out of your main / satellite speakers really reduces intermodulation distortion and makes a world of difference. For me (but other persons experiences may vary), having that dedicated crossover makes integration of low frequency cabinets much easier. I've never had too much sucess with running the main speakers full range, then adding in a sub with just a low pass crossover (which is typically built into self powered subs). 24 db per octave minimal slope helps too on both high pass and low pass.
I have 4 systems in my home ranging from decent stuff to stuff that’s in the garage. Three of the systems have subs and I don’t think I could live without subs, especially on the two critical listening systems I have set up.