The crossover is the one built into my amp, an Onkyo HT-R550, set at 40Hz now. Any higher is worse, any lower and the sub becomes inaudible unless I am listening to something really bassy. Side note, the R20 is wireless only, and I have toyed with the idea of soldering in an RCA jack or getting a new amp for it altogether. Currently, I've modded the soundbar receiver to run the sub wirelessly using a mono to stereo RCA adapter. It has its own crossover but it's not adjustable, but seems set really high. I am sure I am violating many best practices.
The RCA adapter is connected to Amps pre amp sub out