There is some information in the following forum post:
In addition, the chi-square and AIC are calculated as follows:
ChiSq = 2* (LL - nullLL) [Where nullLL is the null log likelihood for the solution]
AIC = (-2 * LL) + (NP * 2)
The null log likelihood is computed by taking the sum of the logs of the number of concepts in each choice task across all respondents. The log likelihood is a bit more complex, but just like in that forum post realize that the data are being coded where things like tasks without responses have been removed, etc. and could account for minor differences.
If you would like to know how it is calculated in more depth, please feel free to email me at walt at sawtoothsoftware.com.