what bignastyid listed is exactly what i was suggesting.
the hdmi would go to your tv (for video) while the optical spdif would go to your receiver (for sound).
the only negative is that you would need to swap your tv input (to the video input) since the receiver unit you have cannot provide it (no hdmi input) but since it has optical input it can play the sound out your speakers. its also rather cheap at $35.
getting a different receiver is going to cost more money (to get something decent you're looking at $150-200)
onkyo isnt a terrible budget brand to go with but i went with this sony for my parents since i picked it up for less than 200. decent selection of inputs, it has an on screen display and it can power large speakers.
http/www.ebay.com/itm/Sony-STR-DH540-5-2-Channel-4K-AV-Receiver-725-Watt-Receiver-/161179613311?pt=Receivers_Tuners&hash=item25870db87f while perhaps not the best of all receivers it is fairly cheap with a large output. so no real issues and setup was easy. not a fan of the tuner but then again i dont like the tuner on my $550 receiver (my personal unit) too well either so no big deal.
edit:
since you have a dvd/receiver combo box... using a different receiver would likely involve getting a new dvd/br player. not sure if yours will send 5.1 out via hdmi when it is designed to be the device outputting the sound via its own receiver/amp. you would need to check (you can always just try it out to see first and get a dvd/br if it doesnt)