Low frequencies - headphone and monitors

[GrooveNinja]

You need bass traps to break up the low frequency standing waves. All of the furniture and egg foam won't do much at all for low frequencies, especially below about 150 Hz. You need a lot of bass traps, and, in my experience, they can make quite a difference. Fill the corners with foam or fiberglass, and the deeper it is, the better.

The 8040's may go much lower in their frequency response, but, as you have observed, it doesn't really help you with getting good low frequency balance. It is actually hindering you.