How Do I Adjust A Subwoofer For Best Sound?

"Coaxial" is a bit of a misnomer. technically, all it means is the speakers share the same centerline.
Typically it's used to mean a two way setup- a woofer and a tweeter...with the tweeter centered.

"Triaxial" is used to mean a three speaker system, even though technically it means there are three axes.

Personally, I like 60 Hz to come from a non-sub driver.
I like it to "punch" rather than "rumble".
...and I like it aimed at me rather than the ground or the wall.
I want to feel that 60 Hz in my spine, not my butt (or my fillings).

...but this has been with 8, 10, and 12" woofers, or at least 6x9's.

Agree asking those small magnet 6.5's to do 60 Hz "with authority" is probably pushing it, despite what the spec sheet says.