I'm assuming that you're referring to SPS's EDI integration?
If so, we have a similar setup with TrueCommerce, but the flow is probably similar. We fulfill in NetSuite and have to trigger a 'manual' process afterwards that creates the data that TC needs to transmit the ASN. A saved search pulls the item fulfillment records that have been processed and TC then picks them up and transmits back to Wayfair.
And yes, to automate, you'll need to script. I've heard that SPS has an addon for that, but I don't know anything about it. TC does not.