Henry,
The DeltaNet online does give more information, but there is no way to access it with a buddy pass. You can ask the employee who gave you the pass if they have access to DeltaNet (also called TravelNET). Not all employee groups have logins yet.

With June you want to be be very careful with the early part of June because that is when school gets out and everyone flees the country. Also....be very careful about using ATL as a backup. There are more options out of Atlanta, however there are MANY more non-revs on ATL flights.

Regarding that seatmap website...try it again, it works fine for me when I click from the forum post.

Happy Travels!