Connecting a sub which way to go

Ha! I came here to give you Paul McGowen’s answer: use a high level input for the sub. I appreciate the logic of it: whatever colorations or sonic signature your amp applies to the signal will also be applied to the sub and the speakers and sub will blend better. 

High level is the way to go, sub then takes on characteristics of the amp as well. As has already been stated. But I'm sure there are good sounding systems with both methods.

WRONG!

This underscores the MISINFORMATION that is often perpetuated on these threads. Paul McGowan DID NOT SAY TO RUN HIGH LEVEL FROM SPEAKER OUTS!

To directly quote Paul: "You want to let your main speakers go down as far as they can naturally. Don’t roll them off. The subwoofer should fill in whatever is missing in the main speaker."

You want to use line outs (optimally left and right line outs to two subs) of your preamp to your subs so that you can integrate them while utilizing the FULL RANGE of your mains.

The beauty of SVS subs is that they have a continuously adjustable crossover that you can fine tune so that they pick up where your mains leave off, maximizing integration. This way you are not constrained by the standard 80 Hz crossover typically used on a speaker level input on the sub, e.g., Velodyne. 

Please watch: https://www.psaudio.com/askpaul/why-dont-your-products-feature-a-subwoofer-output/

Wow chill out. What makes Paul McGowan such a god I wonder.
Some sub mfrs like REL recommend high level, I would trust them as one of the best sbwfr makers.
OP, whatever sounds right to you is best.

This is about the wilfull spreading of inaccurate information, not about Paul McGowan as an expert. REL doesn’t control the subwoofer market. I’ve tried their products and was unimpressed.