You have rather small, easy to drive speakers and a good sub. Based on that you shouldn't worry too much about power ratings as any receiver anywhere near your budget will drive them just fine.
As mentioned by another poster above, the room correction eq's will make the largest audible difference. I prefer systems that eq subs and deep bass as those areas tend to be most prone to room interaction. Anthems ARC and Audysseys MultEq XT32 are some of the most popular and well reviewed. Since you mention a NAS drive as a source, you may want to rule out the Anthem if you want to stream straight from the receiver. In that case check out the Denon AVR-X4000 as it is pretty feature rich, has MultEq XT32, lots of support for streaming, and just about every other bell and whistle Denon could jam in there.
If you already have a good streaming device, and are ok with a few less features and sticking with 5.1, Anthem's new MRX-310 has a very well regarded room correction system with their proprietary ARC system and may be in your price range.
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