How do you know if you need to add a sub (without auditioning one, I mean)?

I’m sorry, first poster. Add an S to the word sub.

OP here. Thanks for the responses so far. Is there a consensus as to how much one needs to spend to get a decent sub that really makes a difference? I’m not saying I want to spend the bare minimum, I’m just interested in a basic parameter.

Erik: Thank you so much. It was very helpful.

Hey, Bruce. I am eternally grateful. I won’t forget you.
I was researching subs and decided that if I gathered enough extra bucks, I’d start with a used SVS PB3000 and take it from there. We have a large, cathedral ceilinged, complex room or I’d aim at something smaller. So I appreciate your right on the mark advice. You haven’t been wrong yet.
marc

I meant sb3000

Fiesta: great idea.
Guy: big sub=divorce.

Wow, what ton of helpful responses.

So what does anyone think of the idea of using a Loki as a very inexpensive experiment to see if more bass even suits me. I know it won’t be the lower register bass and there are plenty of other differences between this and a sub. Nonetheless, I still wonder what someone more expert than I thinks about this idea.
Along those same lines, if someone has a loki with speakers like mine or similar speakers, what sort of Settings did you end up with? Do you adjust them enough to justify having the Loki? Where is the best bang for the buck in terms of the band adjustment?
As usual, I have a suspicion that a lot of these questions are naïve, born of ignorance, or perhaps just unanswerable. It does no harm to ask, though.

61: great information. Thanks so much.

Minorl: I like your idea of testing DB at all the frequencies. Aside from my wondering about subs, I'm sure I have room problems I don't know about since I have almost no points of reference as to how rooms/systems without problems sound.
It's certainly possible (and maybe probable) that I don't need anything more than what I've got, given that I can maximize/improve without adding devices or components.

By the way, I'm pleased that so many posters are really trying to help me vs promote other agendas or make me feel like a dumbass.