Soldering rails in the manner you have described may prove to be an issue with expansion and contraction. Not that your environment's temperatures are going to vary drastically, but solder is not meant to be a structural element. I don't know what metal Atlas uses for it's track, so I cannot give you any suggestions on how to solder it.
I really don't think the joints are what you should be concerned with as far as sound goes. Using some method of sound deadening under the track is more important.
