You have the ability to power the speakers either through your dad's receiver, through your dvd-player/receiver, or through the sub module. Ahhh, choices, choices.
Neither your dad's receiver nor your dvd-player/receiver have 5.1 analog outputs. So, using your dad's receiver isn't going to get you anything, IMO.
Here's what I would try. Connect the speakers from the TR-503 directly to your dvd-player/receiver using the speaker outputs on your receiver. Next, connect an RCA cable from the subwoofer pre-out on your receiver to sub input (one of the 5.1 inputs) on the back of the TR-503 sub module. You'll need to adjust the subwoofer output level on your receiver to get the volumes lined up. You can level the volumes using internal test tones from the receiver (if it has them) or by using a set-up disc, and you can judge the volume either by ear or by using an SPL meter.