Hello, all. Sorry to be bothering you. I am new to this forum and fairly new to high end audio as well and I am in one serious doubt in what would make a better upgrade for my system. I got a pair polk´s RTi10 and one brand level receiver, not in the same level as polk´s loudspeakers. I now am thinking about upgrading my system but cannot decide if i should whether buy a new good quality receiver or a good quality subwoofer. I am thinking of buying the denon avr-1905, avr-2805 or avr-3805. Is difference in price between them worth the money or the lowest one would already be adequate? What are your suggestions on these receivers, are there others on the same price range that could do better for me?
Now, about the sub. What could match my system? I heard polk´s subs are not the best, that there are others on the same price range that can do better than them.

I mainly listen to drum'n'bass and jazz. My budget is of about US$1600 for the receiver and US$1000 for the sub.

Sorry for the long post and I hope you can help me.