Help with setting impediance level for Polk rti a7 speakers

So now you have Infinity Ref 60's! What happened to the Polk's? I doubt you have either!

The POA 2800 has two sets of outputs per channel for driving two pairs of speakers.They are identical. Use either set with your pair of speakers.

The OP has a SS amp! Not a tube amp with multiple outputs! A Denon POA 2800! 

Try both and see which one sounds better. Use that one.

I think you question relates to the amps output.  The amp will “see” the impedance of the speakers and its output will vary depending on what it is ”seeing” automatically.  This occurs instantaneously and continuously as the impedance will vary with frequency also.  The amps specifications give you insite as to their ability to handle different impediance scenarios. The amps will work fine with you speakers.  Some tube amps actually have 4 ohm or 8 ohm speaker connections to try but most solid state amps have only one set to connect to for each channel.  For additional information on your Polk speakers also look at the Polk Audio forum on Polk’s website. 
http://forum.polkaudio.com/

Do you mean you are using two pairs of speakers? 

Ohhhh ok sorry for my amtuerness. So does that means it’s just only 8ohms if I use just one speaker ? But if I use two as a pair then the watts pushed out are 350-400 watts at 4ohms?

You can’t change the impedance level on speakers!