Two subwoofers for two channel music listening

I think you will find the same results from both options you have. Most guys with two channel use the speaker connection because a lot of two channel setups lack the connections needed. 
To take it to the next level adding and active crossover between your pre and amp (pre amp to sub, sub to amp) is best but more expensive and requires extra interconnects.

Right. No difference. Sub bass is mono. Line level or speaker level, same result. Running from one to he next is fine too. I've done all three. No difference. Use whichever is most convenient.

Audio Alchemy says NOT to hook subs up from their speaker binding posts, whereas Paul McGowan (PS Audio) did a video on speaker to sub


hth

Based on the OP's name, only more conflicting information has been provided-PERFECT

Audio Alchemy says NOT to hook subs up from their speaker binding posts, whereas Paul McGowan (PS Audio) did a video on speaker to sub

Right, but the OP specifically stated his subs have BOTH line level AND high level inputs.  

There is an interesting thing about connections, they are all designed such that if the plug fits, it is safe to use. Check it out. Works for everything.  

Technically, both line level and speaker level are the same. The only difference is the voltage. What do resistors do? Resist voltage. So any speaker level anything can be converted to line level voltage by simply putting a resistor in line. A sub that accepts speaker level, this is exactly what they do. Look at the circuit diagram, the first thing is a 20k or maybe 50k Ohm resistor. Or look at a Line Out Converter, this simple box is nothing more than a resistor with an RCA and terminals making it easy to hook up. Or you can do the same with solder in a few minutes. What I did to my amp, which didn't even have line out. So I modded it. https://systems.audiogon.com/systems/8367 Look at picture #26 to see just how simple this is to do.