To make sure I am understanding you correctly, you are not having this problem with at least some multichannel encoded source material, but are having the problem when listening to 2-channel music with your multichannel system? I do not believe that 4 speakers will necessarily make two channel material sound better. In fact, there are at least several reasons that they should not sound as good as two good speakers on two channel material in a well set up room.
1) If your rears are not being actively driven by the amplifier (with only the fronts driven), they can act as passive radiators absorbing and re-releasing energy from the front speakers like a drum skin - smearing transients. Tap your surrounds' woofer cone and hear what happens, and then put your finger on it when only playing your fronts at higher volume if you don't believe me.
2) If you are having problems when the rear speakers are actively driven, I would monkey with the placement of all your speakers so that they are as close to equal distances from your listening position as possible - as the distance differential away from your ear increases for the fronts and rears, you could start to preceive problems with signal arrival time, resulting in a "smearing" of the signal.
3) With some two channel material played through four channels, you may get phase issues at your listening position, where certain frequencies cancel or add, causing the overall sound to be less coherent.
The suggestions above to turn down your rears may be a quick (but not ideal) fix on the material where you are having problems. This is because actively driving the speakers will tend to resist their passive movements driven by but out of phase with the fronts. And by lowering the volume, you can reduce your perception of any timing or phase issues resulting from poor positioning relative to the front speakers.
I recommend not using your rears for two channel listening at all, and for serious listening, turn your rears around so they face away from the front drivers, or even take them out of the room! for multichannel material, try repositioning your speakers to be as close to the same distance from your ears as possible and run your equalization program for your multichannel processor. If these don't help, then you may have some fatal flaws with room set up or configuration and will need to minimally or radically rearrange the position of your speakers and listening chair, and/or treat the surfaces of your room with accoustic tiles or similar.
Good luck
1) If your rears are not being actively driven by the amplifier (with only the fronts driven), they can act as passive radiators absorbing and re-releasing energy from the front speakers like a drum skin - smearing transients. Tap your surrounds' woofer cone and hear what happens, and then put your finger on it when only playing your fronts at higher volume if you don't believe me.
2) If you are having problems when the rear speakers are actively driven, I would monkey with the placement of all your speakers so that they are as close to equal distances from your listening position as possible - as the distance differential away from your ear increases for the fronts and rears, you could start to preceive problems with signal arrival time, resulting in a "smearing" of the signal.
3) With some two channel material played through four channels, you may get phase issues at your listening position, where certain frequencies cancel or add, causing the overall sound to be less coherent.
The suggestions above to turn down your rears may be a quick (but not ideal) fix on the material where you are having problems. This is because actively driving the speakers will tend to resist their passive movements driven by but out of phase with the fronts. And by lowering the volume, you can reduce your perception of any timing or phase issues resulting from poor positioning relative to the front speakers.
I recommend not using your rears for two channel listening at all, and for serious listening, turn your rears around so they face away from the front drivers, or even take them out of the room! for multichannel material, try repositioning your speakers to be as close to the same distance from your ears as possible and run your equalization program for your multichannel processor. If these don't help, then you may have some fatal flaws with room set up or configuration and will need to minimally or radically rearrange the position of your speakers and listening chair, and/or treat the surfaces of your room with accoustic tiles or similar.
Good luck