If I could only use a single CD for this then it would be
Cassandra Wilson - Belly of the Sun .
This as well as being a great piece of music and in my opinion one of the great singers it is also well recorded. It has an image that will show you if your equipment can make those speakers dissapear . On Witchita Lineman the feeling of this group and singer being in your room with you is very strong. There is well recorded acoustic guitar and bass on a number of tracks plus piano and that deep resonant voice which is like being covered in dark an luxurious chocolate.
Added to this there are a couple of tracks which were recorded in the baggage truck on a US to Canada Train which will contrast with the other studio recordings and if your equipment is capable of it give you a real sense of the acoustic space.