Here is a look at the inside of the STX-HD100, as viewing from the front, and above, the unit. As you can see, there is plenty of open space, but that doesn't mean that this unit is a "lightweight".
On the left side is network, audio, and video processing board, and if you look closely, you can see where the rear panel outputs actually connect to the board.
By the same token, you can see the several processing chips that are devoted to various operations of the STX-HD100.
If you are wondering what board is on the right side of the photo, it is the power supply board. You can see where the board connected to the Master Power Switch and the AC Cord. This board provides and regulates all the needed power used by the processing board.
For an additional look, check out the next photo, which shows the same interior, as seen from the rear, and above, the STX-HD100.