Considering your goals the most expansive and enveloping improvement would come from a 7.1 upgrade and no dipoles. Another HL and a couple of Compacts or even a lesser choice for the rears. And since your speakers present an easy load a modest receiver could easily drive them for HT. You really don't have to go nuts to enjoy theater like surround. Your almost there right now.
That's a beautiful space you have.
That's a beautiful space you have.