I do not think you should be losing anything from running the sub off the DVD vs. the receiver.
How big is your room? Length/Width/Height? What are the rest of your speakers?
It is very possible that your whole speaker/sub setup is too small for your room to achieve your desired listening levels.
Where is the sub located? You might try putting it much closer to the listening position.
Sure a ‘bigger’ sub will give you more output. However, if you can get reasonable levels from hooking it up to the DVD player, I do not see why you ca not get that same level from the receiver. I looked at the manual for your receiver, but I did not see anything that stood out to try.
