Speaker boxes are ok, as stated, if your amp can drive both sets of speakers. Although running at least, and probably more than 20' of speaker wire, after splitting the signal through a junction box, with all of those extra termninal connections and the cheap wire inside the box....well, not for me.
You can get the same sonics as if you had a separate front end in the other room by running two long interconnects, balanced would be great, but 20' RCA's should be fine to a second amp(s) in the second room and then normal length speaker cables. If you don't have dual outputs on your pre, then even Y adapters on the output of the pre work fine, with liitle or slight sonic degredation. Although dual outputs on the pre is the way to go.
You can get the same sonics as if you had a separate front end in the other room by running two long interconnects, balanced would be great, but 20' RCA's should be fine to a second amp(s) in the second room and then normal length speaker cables. If you don't have dual outputs on your pre, then even Y adapters on the output of the pre work fine, with liitle or slight sonic degredation. Although dual outputs on the pre is the way to go.