You will NOT need dual subs. I have a single EP600 in my 4,000 cubic foot room. This room is opened up to the rest of the house via a very large staircase. So my theatre room is in essence open to the rest of the house. A single EP600 is more than enough with toms of headroom to spare. You can sell the Earthquake sub \:\) .

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated