Does speaker-level input to sub by pass its electronics?

 To the contrary, I was concerned that speaker-level input might treat the subs as ordinary 15" speakers, but the high input impedance of subs is always stressed as the reason it doesn't stress the amp.

That would be a very odd design!

It's a lot easier on everyone if the speaker input presented even a normal 8 Ohm load as that would require large, and expensive parts, and completely different crossover components.

As Duke points out, it's usually a high impedance input with a voltage divider.  Your amp will see a parallel 1,000 Ohm load or so, and the subwoofer's electronics will see a vastly reduced voltage swing (Say from 50V to 2).

There’s no part of that amp you want to bypass.

If you want to start modding or DIY'ing a sub, consider making your own from scratch.

Um, no, and if you did bypass them you'd end up with no signal.

Besides, the servo itself acts to reduce distortion, so no idea what it is you are trying to accomplish here.

Best,

E