I purchased my RX-V659 from Amazon / WholesaleAV several months ago. The unit actually ships from a Distribution warehouse (not wholesaleAV), the RX-V659 came with all warranty information / cards etc..
I also took advantage of Amazon $ 30.00 credit for getting a Amazon credit card, so my 659 cost less than $ 300.00 delivered. The 659 arrived at my doorstep in 3 days after ordering.
So far I'm very happy with the 659, I'm driving full range 6ohm speakers in a 5.0 setup. Your 4 ohms may create a lot of heat if you drive them to ear piercing levels for extended time. When I first got my 659, I played a lot of "test" DVD's I got off the AVS forum link. These DVD's had cuts from various movies (Master & Commander, Ice Age etc.) for showcasing LFE, Subwoffer, Special effects etc. At listening levels -5 to -0 (very loud) I encountered several times of thermal shutdown. NowThat I have gotten the Awe & Spectical out of my blood stream and now listen to sane levels, I have had no thermal shutdowns.
The 5890 is no more powerful than the 659, it's only the way Yamaha rates the amplifier section for different markets.
The Yamaha's DSP is excellent and I like the fact That I can at a later date add external amplifier power to all channels thru the pre-outs. For $ 300.00 the RX-V659 is a bargain, I don't know how long they will be available as the RX-V661 seems to be the replacement model.