I would negotiate a lower price. As the ad states, its over 2 years old. Offer $1500.
The SS Musical Surroundings simply won't have the tube dynamics of the Manley. It will be quieter(noticeable only when you have the volume at unrealistic levels at idle or quiet passages). That's the only benefit IMO, to the Nova.
Demoed a Chinook in my system. Very nice, especially if you can get that unit for half the retail. I would get the Chinook, listen to it stock for awhile, nice power cord(not expensive) and 2 NOS 6DJ8's if audio nervosa sets in.