My opinion on all of this is this it’s more likely an issue with all the drive pedals you have. If you’ve come from playing guitar, then those pedals may not be voiced brilliantly for bass.
What effects/drive pedals are you using?
Honestly, all the amps you mention are of similar quality and have the ability to get a good tone, they’ll all sound pretty similar with fairly small EQ changes. The Markbass for example, some people talk about the MB ‘character’, but with the filters off, I’ve my LM2 on an oscilloscope, and it’s basically flat.
Anyway, all that to say that a preamp pedal likely won’t resolve the issue, not least because not all FX loops are created equally, some are post EQ (great for bypassing the amps preamp and just making use of the power section), but some are pre EQ (like Markbass), meaning a preamp pedal whether in-line with the amps input, or placed in the FX loop, will simply be adding additional EQ to the amps EQ.
So, my personal advice, pending knowing what other pedals you’re using, would be to buy an amp that you can take around to all rehearsal rooms, because a consistency here will help IMO. Then review all your drive pedals in the context of that one amp, and start building a tone you enjoy!
Si