Need / Want info on the Onkyo receiver

[neos_peace]

Hey blu's. Um after income tax time I'm going to be investing in the Onkyo TX-SR805 receiver. Hoever I ran into a slight delima. I know that it's rated at 130 watt RMS at 8ohms, and 150 Watt RMS at 4 ohms (which I honesatly don't know what that means the ohms that is) But I can't find anywhere what the max is. I need to know that so that I can figure out what type of sub I plan on getting with the unit. I'm thinking a polkaudio sub for it but stil want some insight on that as well. I'm looking for a sub that can really kick, (and I do mean kick I love my bass) It will mainly be used for used fro BD movies and very very occasionally for musci but extremely rarely. Any info wil help. My price range for a good sub is about $250 what are your recommendations.