I came across the board and the topic by chance as I have been asking the same question.
The best answer I found so far is from "Systematic Theology" chapter 23 "The Essential Nature of Man" by Wayne Grudem. The outline of the chapter may be found at
http://www.christianessentialssbc.co...007/041507.pdf. The lecture audio may be found at
http://archive.scottsdalebible.com/a...415WGrudem.mp3
Also I found a helpful article titled "What About Watchman Nee’s Teaching on Soul and Spirit?" by Gordon Ferguson at
http://gordonferguson.org/articles/w...ul-and-spirit/