The Power Switch is confirmed.
The Power LED is confirmed.
The Reset Switch is confirmed.

Maybe the HDD Activity LED is in fact polarized Speaker Leads. These pins
are so tiny it is hard to tell. But it is only these that need closer
inspection.

This is a URL to an image of the MX330-X front panel connector:
"How-to-connect-case-cables-system-panel."
https://assets.rockpapershotgun.com/...stem-panel.jpg

Note there is no HDD Activity LED between pins 1, 2. They belong
elsewhere. On the GA-EP45-DS3L they belong on pins 20, 14. In this image
they appear on pins 18, 14.

Now to sleep.

[correction, even and odd # pins are on opposite sides of header]

Houston, we have a problem. HDD Activity LED pins 1, 3 and MX330-X
connection is fused and clearly marked HDD Activity LED & polarity. While
Power LED MX330-X connectors are not fused, polarity marked and might be a
candidate to connect to pins 20, 14, they are confirmed as Power LED. When
ON the Power LED glows steady and does not pulse as expected for front-panel
speaker beep. Maybe an email to Cougar is needed. Strange, this problem was
not flagged in reviews.