I would not add much reverb either if any. What I would do is give more space to the instruments by panning them more around the center. A little offset from center for piano, and mixing the horns (saxes then) like an orchestra would be live or at least off of the center until spread to the left and right, different parts in different pans.
Imagine placing the instruments on the sound stage and adding the amount of reverb (or echo) that makes it a 3D stage perhaps.
L and R speakers are suppose to be a 3D sound stage with some sounds a little more distanced from the single point say of the conductor than others with a bit more reverb and perhaps a bit less volume. Well, the imagining of such an environment, including it in the place perhaps if you can where it will happen - to listen to it there also.
Right now to me it sounds too left and too right with a hole in the middle. The voice to me just can not be the only thing there even if it is a bit more reverb or what I would do with some of the parts pan it more towards the middle like 50 left - 20 right for a part or 50 right - 20 left for another part and so on.
The stage is what you make it.
??
Yes, I always add questions marks, because the end result is up to you, not me.
And it all has been done before, but perhaps a video more in the center of the sound stage would help, but again, here's something different.
http://www.youtube.com/watch?v=qukRwWSXYXw