Originally Posted by gurkey
Sorry, but i don't know the specs for the B&W speakers.
But as stated the Onkyo and Integra AVRs are generally specified (and stable) for impedance values down to 3 Ohm. You might check the data sheet for the B&W speakers though, to make sure it fits.
Most modern speakers (with some rather exotic exceptions) are defined as 4-8 Ohm mean value, which would fit.
Integra/Onkyo list very few AVRs or stereo receivers as 4ohm capable. Integra's own website shows the 5.9 as being rated for 8ohm speakers only - check the specs
under 'features' - neither the 4 or 6 ohm spec is checked off - meaning it isn't recommended for those speaker loads - meaning the amp section may not be as good as other stereo receivers. Both of the Harman Kardon receivers I mentioned above are 4ohm rated.
B&W speakers are almost always 8ohm - as is the 686. The Integra 5.9 is pretty much an Onkyo TX-8555 IIRC. At any rate the Integra should work fine for those speakers. As would the Marantz 4023 - or just about any other stereo receiver you might want to buy. I mentioned the lack of 4ohm rating for that Integra since you might want to buy some 4ohm speakers at some point in the future.