I discovered another multilevel multiprocess software, Sabre (and its R implementation SabreR). It seems to be very efficient and well integrated with R. It is also possible to run it (a parallel version) on a cluster. Looks very promising. I should be able to use it for serious exploration in a day or two.
Unlike aML, Sabre is still under active development, which means that new features, such as more finite mixture modeling capability, hopefully may be incorporated into future releases.
Home page: http://sabre.lancs.ac.uk/