I have no experience with portable macerators, but if your Excella is "stock", then you likely have the Thetford sewer fittings rather than today's much more common Valterra sewer fittings. You can still buy the Thetford fittings. They're not as common in retail stores, though they're widely available online. I've noticed that Camping World does not routinely stock them. There are times when you may find it beneficial to use the Thetford to Valterra adapter, such as when you're using a hydro flush or similar contraption, or as in your case when you're trying to connect your new hose to the Thetford fitting on your Airstream. Unless you want to make the complete conversion, you can use the adapter when you use the hydro flush, and buy the Thetford hose end fittings to replace the Valterra fitting that's on your new hose.
Amazon.com: Valterra T05-2285VP Thetford to Valterra Universal Adapter: Automotive