Connect the DVD and the set top box to the TV via HDMI. You can then connect the TV to the receiver via optical audio. The MD player being audio only can be connected directly to the receiver.
An alternative is to use digital connections from the set top box and the DVD to the receiver instead of the optical cable from the TV. Sometimes this is physically easier to do.
You may want to run a video out from the receiver to the TV so that you can access the on screen menus of the receiver. Composite video is fine for this.