There a million things you can always do. However, right now, I feel you have it well connected. Spend time with it, tweak around and enjoy burning it in.
Just 2 things though, I would use option 2 to connect. Second I would set the gain/volume while playing music and not frequencies. Play a track with repeated bass notes and then increase the volume on the sub till it just about starts to fill. Same thing mentioned in the video. Nothing else needed. Don't worry about the null in the 20-40hz range, its due to the room. You could try relocating the sub to another spot, but that can be done later.
MaSh