I definitely want to follow what you are saying. What is your sub? What are low and high level inputs on the sub? On my current sub I don’t even have speaker inputs.
That definitely narrows your setup options then. Just use the inputs you have and experiment with placement, and gain settings til you like it.
I can’t post pics on this forum, but you can certainly google to see the numerous types of input (and output) options on the plate amp on the back of many active subs.
My sub(s) are Definitive Technology PF-1500 and Dayton SUB-1200. Without getting too wordy with details, both are active subs with plate amps built into the backs. Both offer a couple of input options (many do). 1. RCA phono jacks that are low level inputs from a line source like a preamp output. 2. They also have high level speaker inputs that accept the speaker output from an amplifier....they basically reduce that amplified signal down to a lower voltage that’s similar to a line level voltage so that the sub’s amp can then re-amplify the signal and drive the sub, so the main amp only has the responsibility of driving the main speakers. Many subs also have a variable low pass (and high pass) crossover filters, gain knobs, 0 and 180 phase options, etc.