You need to insert a silent track between each track as you specify them so you end up with something like:

sox track1.wav silence.wav track2.wav silence.wav ... output.wav 

You can do that manually (as above), or we can loop the current directory with an inline for-loop. Something like this should work:

sox -n -r 44100 -c 2 /tmp/silence.wav trim 0.0 2

sox $(for f in *.wav; do echo -n "$f /tmp/silence.wav "; done) output.wav

The silence-generator is stolen from here.