This thread has been helpful as well as a few other. Pitching in on what I have done to my car.
Just got my 2022 CX30 Select audio upgrade with a mini powered sub professionally installed.
Infinity Basslink Mini underneath the driver seat. When asking the shop, they said it is the Infinity equivalent of the JBL Basspro Nano, which was my original choice.
I asked the shop how it would wired and they confirmed that most likely method is tapping into front speaker wires.
As previously posted, there is a grill that house the amp under the passenger side, so the tech could not fit it under there, which would have been my preferred location. Now I get some extra vibrating "effect" on higher volumn but it is not too bad hah.
I like how how it turned out, as I just needed the lows. Stock non Bose had good enough mid and high for me.
Got it done for 399$ for labor and parts including tax.
Good luck all.