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.
Taking AIF as the way to go. Which tables should be populated in order to have the registrer Transactions and be able them to post Statements?
You should populate the RetailTransactionTable and related tables (RetailTransactionSalesTrans, RetailTransactionAddressTrans etc. tables). in the channel database. You can then use the standard AX P-0001 scheduler job to pull the transaction into AX and follow the standard from there.
If you take a look at the standard channel database schema for AX 2012 R3 you'll notice that there are many standard stored procedures and views. Artifacts used by CRT (Commerce Run Time) are part of the "crt" security schema, others are part of the "ax" security schema. The standard AX POS client also makes use of those artifacts to read from and write into the channel database tables.
In one of my last projects I have simulated the exact same behavior with Microsoft BizTalk - we also tried to re-use as much standard channel database views and stored procedures as possible. For the real time part we also leveraged Real Time Service directly from our BizTalk processes. So in the end our integration to the 3rd party systems was actually an extension to standard AX/Retail CDX. It works perfectly fine, requires 0 to minimal customization in AX and makes your 3rd party POS and E-commerce channels behave as native AX client. So you can fully leverage standard AX Retail for your 3rd party sales channels.
I have written a series of blog posts about the integration on my blog. Here's the landing page for this series of blogs. I've also written this blog post to highlight why I would not leverage AIF for Retail integrations.
I know it has been a while since you posted this, but if it doesn't help you for your current project, then hopefully in a future project ;-).