I didn't realize I asked a stupid question until much later, sorry folks.

(Duh you need power for a preamp!)
No you did not. No need to apologize. It is a valid question and my guess is because of the following. As a recovering engineer, my experience is that to get a fruitful answer, it is best when asking for technical solutions to outline your requirements or end result first and define your use cases, outline your current resources and budget BUT do not get into solution space, As you may have observed, your methodology was scrutinized and faults were outlined rather than help you with your goals. Budget is important because people will either recommend top of the line , or tell you to make do.
Now why regarding the power question, it maybe because:
Phantom power is used to power many condenser microphone, electret mic, bass built in preamplifiers ( like alembic)s and DI boxes using one cable usually an XLR and sometimes a stereo cable TRS ( Tip Ring Sleeve ) -- so reasonable to be confused. For bass amplifiers more than 99% do not do this on the FX loop. There are however some amplifiers that supply 48 volts to microphones usually amplifiers that support acoustic instruments. Some like the AER provide 12 volts from the common 1/4 jack. Again not common and usually preamps and effects need their own power supply. Another thing that can leas to the confusion is that some old amplifiers have power outlets as well and you can definitely use them to power you rackmount. Last but not least is that some amplifiers provide 5vvolts via USB and some pedals and devices can be powered by USB.
What may have been confusing to us is you are mentioning 2 amps. meaning 2 boxes that can be used to amplify music loudly and connected to the speakers , Is this what you meant or did you mean 2 channels in your amplifier
If you do have have 2 amplifier connected separately to 2 speakers, a rackmount preamp, I would set it up like this.
Active ABY box with phase inversion, Why active because it will ensure a better quality split no signal loss and no cross talk,. I recommend the Radial TwinCity ABY or anything from SaturnWorks. They have the option of switching to A or B and combining them as you already now.
Bass to ABY input
A output of ABY directly to the first amp - do not play it yet
B output of ABY output to input of rackmount EQ powered up separately, Output from Rackmount to the FX return of your second Amp, Now rackmount preamps may have pro level +4dB switch in the back , You probably need to play with that, If it has a out level start low and increase. If you have issues try switching it to the front of the amp, Once you are happy with the sound, Oh yeah press button on ABY so that B output is active
Test Amp A and adjust with B volume. I suggest start with clean first and keep volume similar,, Now swatch them on the same. If you notice a dropout of volume then flip the phase switch. Some ABY like the TwinCity also comes with a drag control and Satrunworks provide volume controls as well. But phase is the key here. The BigShot also has a ground lift and if you hear a hum when combining flip that as well,
If both amplifiers are working normally then you can start adding dirt or playing with , Remember EQ to taste and you may encounter phase cancellations and all sorts of filtering and the sound may suck
I use 2 amplifiers all the time mostly for guitar, sometimes for electric bass but use them for my double bass setup because I have 2 sources, mic and pickups and my music relies on that setup. I rely on my active ABY Switch, I do find that many bew effect boxes are capable of internal splitting and do much more than 2 amplifiers and much easier to work with for electric bass.
One caveat, even though we have helpful and technical people here, some even at the top of the industry in their field, this is an ENTERTAINMENT website for bass enthusiasts, there is no implied consultancy at all but the answers here are better than AI or internet lore. If it does not make sense, ask again, do not take rough answers as personal
Lastly DO NOT CONNECT BOTH AMPLIFIERS TO THE SAME SPEAKER OR SPEAKER STACK. You will destroy both of them and the speaker/s, maybe even before power up,