Angelo, the ASR files [*.asr & *.srd map files, and en_US.srd] from my 3597LM US unit work fine in my 3590/3490/2595 AU units with unlocked NA map. But i didn't persevere in trying to use TTS3 on them, TTS3 will not work in any series before 2013 and will crash them as you point out, although i didn't brick any unit.
However, everything works normally using ASR files from my 3597 in the ASR capable 2012 models with TTS2. Unless something is different in BR to AU localisation or i've misunderstood you, my experience is that it's simply not a problem to use the asr files from 2013 series in 2012 series provided you only use TTS2. If your plan is to continue trying to get TTS3 working on 2012 series i'm happy to help you with testing, just PM me.
I note the concern with pt_BR.srd not being offered to non-BR localised units, my 3597LM US was not offered Karen or Lee in TTS3 or au_EN.srd either at first but with later fw they're now offered. However, I initially obtained the AU TTS3 voices and srd from other sources and they worked no problem on the US localised unit.