@david396
I just replaced the stock speakers with a pair of Klipsch R-50M bookshelf speakers. As stated by Jim Beletti, the speakers are accessed by removing the fireplace drawer. I removed the old speakers and the stock mounting plate with grill cloth, added an extension to the shelf to mount the speakers on, which put them at the right height to align with the opening in the front. The grill cloth fits just about perfectly into the opening. I also added a hanger bracket to take the weight in the back. See photos.
Now I need to replace the inferior Jensen head unit with something that has an optical audio input so I can route the TV through the new speakers...