I have recently implemented Direct Access and in the course of my testing I found that I was unable to download any applications from the Application Catalogue from my Direct Access client.
The solution is simple, you need to add the IPv6 prefixes found in the client properties to your boundaries \ Boundary groups in SCCM.
In my IPv4 environment the IPv6 prefixes property on the client tab was blank until the client had actually connected via Direct Access. Once it had, the properties were there. I added all three IPv6 prefixes as shown in the screenshot below.
Don’t forget to add the IPv6 prefixes to Active Directory Sites and Services if you have Windows 7 clients! (See here for info)