The best way to be "enveloped" by sound is to be surrounded by speakers. Therefore, getting a receiver or pre/pro with multiple channels will provide "surround sound" and the more channels, the more enveloping the surround sound. 5.1 is good, 7.1 is better, 9.1 better still and 11.1 is the best that is currently available. Of course, you'll need speakers for all those locations also. Therefore, the question is not which is more important... both are essential to the experience.
Now, if you're just talking about 2-channel reproduction, then the speakers will have the biggest impact on the soundstage width. Still, there is no 2-channel system that is "enveloping" unless it uses some kind of sonic trickery.
Lombardi said it:
Perfection is not attainable, but if we chase perfection we can catch excellence."