I am interested in trying to understand the desired approach in trying to integrate a 3rd party POS system with AX 2012 R2 Retail HQ.
My questions would be:
I think better option would be to use AIF and take required data into AX HQ.
Using the AIF services to integrate 3rd party POS to AX is the most optimum solution.
Don't ever try direct injection of data to sql, you may miss on some shared tables.