Cleaning contacts can be good, however, playing for a few minutes, then cutting out is not a dirty contact issue IMO.
Speakers, two pairs? Do you have the receiver's manual?
Unless you have a selector up front for speakers A, or B, or A+B, it may be that you are only supposed to use one, or the other speaker outputs, not both.
Often they are for different OHMs, i.e. a pair of outputs for 8 ohm speakers, or, use the other pair of speaker outputs for 4 ohm speakers.
.............................
Efficient speakers, high sensitivity?
I would hook up only one pair of my most efficient speakers, see how it is. Even small speakers from your office temporarily, just to see if it makes a difference.
Speakers, two pairs? Do you have the receiver's manual?
Unless you have a selector up front for speakers A, or B, or A+B, it may be that you are only supposed to use one, or the other speaker outputs, not both.
Often they are for different OHMs, i.e. a pair of outputs for 8 ohm speakers, or, use the other pair of speaker outputs for 4 ohm speakers.
.............................
Efficient speakers, high sensitivity?
I would hook up only one pair of my most efficient speakers, see how it is. Even small speakers from your office temporarily, just to see if it makes a difference.