If the receiver has an auto set up don't use it.
Connect the front pair to the front speaker terminals.
Connect the middle pair to the surround speaker terminals.
Connect the rear pair to the rear surround speaker terminals.
Set up the receiver for 6.0 operation in the speaker set up menu. Set the front, surround and surround rear speakers to large & center and sub to none.
Set the speaker levels all at the same 0 setting since you don't want surround sound but evenly distributed sound. That will probably be the default setting. The distance setttings should not matter.
Select the multi-channel stereo mode for each input so the receiver will play all the speakers in stereo.