I think the problem is the SharePoint workflow. I think that if we remove that piece, the rest of the puzzle pieces will fit together nicely.
In general, these are the necessary steps:
1. Modify your InfoPath form template such that is submits to the DBXL Document service. Remove any connections that submit to SharePoint directly.
2. Create a new document type in DBXL using this xsn form.
3. Create SQL mapping.
4. Create SharePoint mapping. (Note: You can use the same SharePoint form library you were using, but DBXL needs to own the mapping, so you'll need to empty the form library first and allow DBXL to recreate the documents. Of course, it's safer to simply use a new SharePoint form library.)
5. Submit one document to test your SQL mapping and SharePoint mapping. Tweak (#3 and #4) as necessary until you are satisfied with the mappings.
6. Save your existing xml documents and import them into DBXL. I wrote some steps today to cover one way to do this. The documents will be auto-mapped to SharePoint and SQL (but if they aren't, a quick Reshred All will do it).
From reading your other questions, it seems like you need DBXL to perform a SharePoint-UPDATE operation; that is, DBXL needs to inherit the workflow and the existing library/documents. I don't believe DBXL was designed specifically for that scenario, because DBXL needs to own the xml documents. Patrick wrote a blog post that may be related, but it concerns SQL. Read it here. Perhaps he can provide more of a philosophical perspective next week.