I have an Onkyo receiver too but I forget which one. I have a headphone jack lead permanently plumbed into twin rca's on a spare input so anyone can come along and plug anything into it. I used to have a very long lead from the pc in the next room which I could control from my phone by WiFi, but since that went bang I have been pc free.
I doubt that you could use Bluetooth from anywhere in the house (unless it is a very small house) because the range is limited to about 10m, less if things like walls are in the way. I did used to have a stand alone Bluetooth speaker but tbh, it was terrible, the actual sound quality was good but there was always a very noticeable background hiss whenever it was used wirelessly.
If you do want to go wireless then look at HTC's Media Link HD, it is designed to plug into a tv via hdmi to mirror your phone display, but if you route the hdmi through the receiver, audio should be no problem. Haven't got one myself yet but it's on the list, so can't comment but it's gets very good feedback on Amazon and such. Someone on here is bound to have one so they can tell you if it works or not. Not sure how much it is in the US but in the UK it is about ?80 from HTC or ?50-60 on Amazon.