I think you will find that converting sRGB to aRGB will give you no benefits at all as the information has already been discarded when you took the picture. ( sRGB has a smaller gamut than aRGB ) and you can't put the information back by converting.
As far as I'm aware the vast majority of labs will want your images in sRGB but as I do my own printing and don't use labs I can't be 100% sure.
Why not do your shooting in RGB so you have the maximum amount of information available ? you could archive the original file incase printer technology catches up and then you could print your images in all there glory and it's simple to convert to sRGB after editing your images.
Hope this helps.
Steve
