Ok, so assuming these are your only speakers and you don't have a sub, towers or anything, here's my recommendation.
Wire up 1 pair of speakers on the front terminals
Wire up 2 pairs of speakers to the rear terminals
Amp switched to 4 channel mode
Leave both switched to full
turn down the gains and slowly turn them up
If you find there is too much bass coming through, turn on the low pass filter, put it to around 60-80hz this will filter out the sub bass, but leave in the mid bass.
If you find there is too much highs coming through (unlikely) turn on the high pass filter and tune it down until you are no longer hearing it sound tinny.
Depending on how you have the speakers hooked up, you may have too little resistance on the amp and it is getting way too much signal. This setup would put your fronts to 4 ohm and the rears to 2 ohm.