Xin did flip the input and output jacks early in the run. Make sure you're using the right ports. If it's dead, you're not going to break it any more than it is now.
Also, make sure your jumpers are in place. Specifically the Crossfeed jumpers. They are the ones that have 3 poles. If those aren't making a connection, there is no signal path for the sound to travel down. It might
be a long shot, but it's a thought.
Make sure that the opamp is seated properly, and that the jumper wires appear to be in place. Pretty much just make sure it looks like the picture on his website. Maybe your amp just got tossed around in shipping and something came loose.
Xin has been very good about repairs, replacements, special adjustments, etc. Contact him and I'm sure he'll fix your amp right up.
I've had the mini since December, at it is definitely worth keeping.
good luck
-Jeff