I actually have both attached to my system now. The Nova is a recent addition and the Jupiter will be headed to my second system.
I would characterize the Jupiter to be a "smooth" sound and the Nova a more detailed sound. Overall the Nova has better high end detail, bass definition, imaging and depth. Not surprisingly the Nova has a more open sound and creates a larger soundstage. Also the Jupiter does not have the dynamic range of the Nova. The reviews of both players sum up things pretty well.
The Jupiter is still a great sounding unit at around half the price of the Nova. If you can afford the extra cash the Nova is the better player.
Auditioned with:
Simaudio P3
Simaudio W5
Dynaudio Contour 3.3's