I would add an active crossover to what ever sub you choose. It is as important as the sub (more so IMO).
this apologue model from Sublime acoustics is only $600. I use the K235 that adds balanced inputs/outputs for $1,100 but the units are 95% the same. In my system (McIntosh/JBL 4367) is it transparent with no loss of detail to my ear and no added hiss.
https://sublimeacoustic.com/products/k231-stereo-3-way-active-crossover