Antonio, Just use the AVR-630 that you have. It would be too costly to move to another receiver. However, you could consider getting a separate 2-channel amp to drive your Polk RTi10 speakers. Going the separate amp route might be the cheapest way - vs. going with a new receiver that would provide possibly only a nominal difference in power.
I have the little brothers to the Polks that you own - I have the RTi8 speakers. For me, it took a few months of using them before they loosened up and started to sound pretty decent. Had I sent continuous power to them, I'm sure they would have been broken in within a week's time-period.
Speakers take time to loosen up a bit so their true sound can be revealed. Nothing is essentially wrong with the sound of a "just out of the box speaker." However, the sound can, and does, improve with time.
Well it takes them about a minute or so to loosen up. As to whether the sound improves, that's a function of you getting used to them or not. A lengthy thread on speaker break-in can be found here. Not every speaker is going to work for you despite that thousands may feel otherwise. My general position on this is if you don't like the way the speaker sounds after working with it at home, don't keep holding on to it past the store's return policy so you can get your money back.
Apart from that, you may need to work on the speaker placement. A series of articles regarding that can be found in the thread Can You Make Your Sound Better.