I like my Gk Mb112 with extra 112 powered cab.
Right now I'm running rounds on my basses.
I get some good tones out of it all. I've EQ'd 'til there was nothing left to EQ...either on bass or amp.
Tried Boss EQ pedal. Tried Eden WTD. Tried B1on Zoom.
But I was looking for a little deeper low end. By that I mean the tones I get now are good...but...I was looking for something a little deeper and richer.
Tried all kinds of string:- Flats, tapes, half-rounds, rounds...the list goes on.
Flats and tapes give different tone than rounds but not any "deeper" tone than rounds.
In a couple of instances rounds outperformed flats by a significant margin.
They all sound good mostly but not as "deep" as I'd like. Hard to describe.
Right now I'm using:-
Squier Jag SS...stock pickups with rounds.
Squier Bronco..P/J Red Lace sensors with rounds.
Ibanex Mikro 4-string...stock pickups with rounds.
So amp is 2 x 12.
Go bigger amp? Different speaker size? New different pickups?
Did you try heavier gauge strings? Ticker strings will give a little deeper tone, but if you really don't want to change gauge then ignore the suggestion.