Hi, exactly what sox command are you giving? I'm on my phone till tomorrow
and can't check, but the idea with jack is that sox will expose some output
ports which you should connect, with qjackctl for example, to your
soundcard.
Also, I was using sox too but was reccomended by many here ecasound, and
for the little I used it it did indeed seemed better (audio flow is more
clear)
Have fun,
Renato