Hi Kurt,
Glad you figured it out. I'll reply to your post in case there are other users who want to accomplish this as well. Like many things in Method there are many ways to acheive this, here's what I did.
To start, I strongly recommend making a copy of the CRM_CaseList_withActivities report, so you can revert to the original if needed. Then, you can create a Formatting Rule which will apply to the Headers GroupHeader2 and Detail. You can use the Variable: DataSource.CurrentRowIndex. This will be used to filter out all rows except the first. Your condition will look like:
[DataSource.CurrentRowIndex] != 0
Note that 0 is used since indexing starts at 0. This condition will set the Visible property to No. After this, apply this rule to the headers mentioned above.
The final step is to change the sorting so that the newest case is first. Click on the detail header, and modify it to sort RecordID Descending. You can delete one of the RecordIDs since it's not necessary:
-Russell