Sorry. You are hearing the DolbyDigital surround track and not the DVD-A track.
Get whichever Oppo meets your price. Be prepared to hook the player to a monitor in order to play DVD-A, as every disc brand has a different path for the menu to be able to choose surround or stereo (or DVD Dolby). Sony never supported DVD-A(MLP) in their players, because they created SACD. However, HDAD discs (24/96 LPCM) will play in any DVD player.