@millercarbon is right about different albums over time. I am a musician, DJ and sound engineer. This is where the sound engineer comes in. Play any of your jazz & R&R records at a normal (for you) listening level. What you want to do is act as the sound engineer because you ARE the sound engineer. But only for the bass signal. You want to make the bass fit in with the music. Or more accurately put mix the bass so it blends well with the other instruments that are playing. Its really that simple. Don’t complicate it. Mix the bass response to fit with the music. Remember that.
The gain & crossover points work in conjunction. Gain/volume is easy. Now the crossover may be the tedious part. But what you want to hear from a bass guitar is a little bit of overhang on the notes. Not much. But a bass note that stops on a dime is not how a real bass sounds. It has a little bit of overhang or sustain. But only a slight sustain. I’m talking fractions of a second. This is done with the crossover. Set it just high enough to get that millisecond of the bass note sustain/overhang. I hope you get the concept of what to listen for and the simplicity of the job. BTW it takes some time. You need to get the mix roughed in. Then sit and listen for awhile until it becomes clear what is missing or what needs reducing. But listen to more than just one song or even one album. IOW take your time.You will get it