Choir verses Piano

I am teaching myself to use Sibelius and I'm writing a short 4 part choral piece using Garritan Aria Choir in John O' Sullivan's Blue JI tuning.
(details of the tuning http://chrisvaisvil.com/?p=317 )

I present to you the same piece of music which is pretty chromatic and I think sounds completely great as a choral piece despite it.
But the piano shows the "rough edges"

choir only
http://micro.soonlabel.com/blue-tuning/Aria_Soon.mp3
GPO piano only
http://micro.soonlabel.com/blue-tuning/Aria_Soon_piano.mp3
choir and piano mixed
http://micro.soonlabel.com/blue-tuning/aria_soon_Mixdown.mp3

In any case, in the choir setting, I feel I can do pretty much anything I want.
(Though I am getting a bit more conventional as the piece progresses.)

Chris