I'm not really sure why the ASS was involved in this. I feel like it might have been simpler to just do everything in the ASX model, to keep things cleaner. Also, the IPC blocks for this stuff (in both ASS and ASX) are not on the top level of the model. I had thought that this was expressly forbidden (although I'm not sure why). I'm emailing Jamie, to see if he remembers what, if anything, is breakable if the IPC blocks are down a level.
I'm not sure if it's forbidden by the RCG, but you should definitely NOT do it. All IO, whether it be between ADC/DACs or IPCs, should always be at the model top level. That's what keeps things portable, and makes it easier to keep track of where are signals are going/coming from.