In terms of sound quality, what is most important are the speakers, not the receiver or amplifier. Unless the speakers are a difficult impedance, or are terribly inefficient, or one listens at volumes loud enough to do permanent damage to one's hearing, in an ordinary room, just about any receiver or amplifier from a reputable company (e.g., Yamaha, Denon, Marantz, Pioneer, etc.) will be adequate. Of course, the sorts of decoders you want will depend upon the source material you will be playing.
And for speakers, although reviews in which actual measurements are taken can be useful (particularly for removing a model from consideration), you should listen to as many different models, from as many different companies, of as many different types (e.g., ribbons, horns, domes, whatever), as you can stand, that are within your price range. The reason is, there is no such thing as a perfect speaker, and so it is a question of which virtues you require and which vices you can tolerate.
In my opinion, if you don't have a lot of money, it would be better to get a good quality 2 channel system than to get a surround system, but some people feel otherwise and obviously their choices reflect their preferences on such matters.
