Typically, you hook the left and right pre-amp outputs (presuming the 805 has them, if not, you can't do it) to the amp's left and right inputs and hook the L/R speakers to the external amp.
Well i made a mistake i thought this receiver would be the cats ass. But as far as listening 2 channel audio it sucks. So i got to thinking add a amp and then i could use both pairs of my RTi8s in 2 channel. jerry
You can't just hook stuff willy nilly like you seem to have in mind. Maybe you could explain why the 2 channel "sucks". You might be doing it wrong. Surround receivers can be pretty complicated and it is very easy to set them up wrong if you aren't educated on their use.
If you hook a second amp to the pre-out jacks and put both it's speakers and the the ones for the same channels in the same room, they will all make noise, but your receivers auto set with the remote microphone will never be able to adjust. For dolby digital you must set the speakers up as shown on the diagrams, let the receiver self adjust and that's it.
Now if you want that second amplifier and speakers to go in another room then that is a different story. Hooking that to the preamp outs for left and right front will also have problems. Unless the source is plain stereo, the valuable information and sound will be missing. Most notabily when a Dolby Digital is being used then almost all dialog comes from the front center and the remote speakers would miss that entirely.
If you want a seperate amp in another room to have plain stereo then you need a receiver that has a second zone output. The second or third zone will have all data regardless of the input source as the receiver knows that the final output is plain stereo and will internally remix the input source for the zone 2 output to plain stereo. I use zone 2 on my Yamaha for a feed to the whole house audio system and also to drive a pair of headphones.
I agree with John. The Onkyo should have no problem with the Polks, even if they dip low in impedance (which they reportably do), the Onkyo is THX Ultra II certified and can handle down to 3.2 ohms stable.
Did you use the Audyssey EQ? Did you set the Polks to small with the receiver's x-over set for a subwoofer (typically around 80hz). That Onkyo is a fairly complex receiver, and adding an amplifier to it won't likely make a lick of difference unless it's a tube amp.