mlacek , gooday
, I have a 7.1 in an 18x14 room . no problem. your seats need to be 4ft from the rear wall . My screen is 106" . 120" may be a little on the large side . A small room that size needs to have have a lot of absorption in it . like carpet , rugs , drapes over the walls etc . Let us know how you go , Kind regards , Alan Monro .