I've heard of setting the volume of multiple subs with one output on the receiver, by measuring each of them up close to isolate each, but not inside the port. Instead a few inches from the center of the cone. But then the over all sub out trim on the receiver is set from the listening position.
If the receiver is doing the bass management, the cross over on the sub should be bypassed, or set as high as possible. Setting it to 80 not only multiples the slopes, but also could remove LFE content stored on the disc which can go as high as 100 Hz, and won't be sent to the main channels.
I do believe that without the port plugs, SVS subs should have their tuning set to 20 Hz. It's only when converted to sealed should the tuning be lowered. So that seems to be the only thing he got right.
I'd be asking for money back.
