If you group then by the model of the receiver then the more expensive packages with each model of receiver tend to have the better speakers. Though that isn't always a given.
In terms of receiver model the higher number generally means more toys to play with.
Basically down to you whether you need all the features on each receiver. I doubt you'd hear much if any difference in sound quality. The 616 may go a touch louder then the 515 but I doubt your neighbours would let you run the 515 flat out much less the 616
As for 4k. Lets put it this way, if you can afford a 4k telly at the moment you wouldn't be looking at systems this cheap
Look at systems based on Yamaha, Denon and Sony as alternatives to Onkyo. I have an Onkyo system, closest in that list to mine is
http://www.richersounds.com/package/...deals/pah01530
The speakers are very good and I assume the receiver will be as good as it's predecessor that I have.
