I'm going to go out on a limb and say that ProSeries has the correct way to do it for 2018.

On the "front" of the 1040 Postcard next to the Paid Preparer info there is a checkbox for when the preparer is also the 3rd Party Designee.  On my test return that is correctly checked when I check the box on the Info Wks.  The "new" instructions for that line in the Info Wks say "if checked, do not complete designee information".

I *think* Schedule 6 is only required if you're using a non-preparer 3rd Party Designee, in which case you'd NOT check the box for preparer and fill out the three fields for name, phone, pin, then voila, Schedule 6 appears.

Rick