Not sure why anyone would have AP in one ERP system and AR in another (unless you have 2 companies with 2 different systems who were acquired..etc). You may want to consider the following:
You could potentially try a multi source execution for OBIA where you source from PSoft for 1 module and AR from another. This would ONLY work if you consider both systems as 2 separate financial data sets which do NOT share the same dimensions etc. If so, each would have its own unique DataSourceNum ID. You can configure each of them independently and schedule loads that alternate. You CANNOT share any confirmed dimensions unless you have a Master Data solution in place (example...SUPPLIERS and SUPPLIER IDs are the same in both systems)..but I highly doubt this is the case as very few companies have the maturity to do this. Anyways, bottom line is you can load both to ONE DW either as separate loads or a multi source single load. It is something you want to consider doing carefully. You will also need to configure each separately based on each system (e.g. Calendars, Aging Buckets, etc). This all depends on requirements.
You may be better off trying to consolidate your financial ERP modules into one system as a better long term solution.