Jazzman,
Thanks - I saw those instructions on pages 5-19 to 5-21 in the general manual, but they don't apply to the head unit in my car ('17 Touring HK with NAV). The actual display menus in my car are different than what appears on those pages.
The HK/NAV unit for 2017 (and possibly 2016) has its own manual that is separate from the general manual. Pages 99-101 of that manual refers to an "Automatic Sound Levelizer" that appears to function as a speed sensitive sound adjustment, but those functions don't appear in my unit (they are grayed out).
The Outback thread that I included in my earlier post discusses this anomaly. Apparently, there are multiple audio unit variations, and not all functions listed in the manual may apply to a given head unit. According to the Outback thread, the HK unit may have a "built in" speed volume control that is not adjustable.
Of course, someone else may have more information on this.
JFM