Response from AVID:
Please keep in mind that USBpre2 is not a supported audio interface for Pro Tools based on the following chart:
http://avid.force.com/pkb/articles/en_US/Compatibility/Pro-Tools-HD-12-Approved-Audio-Interfaces-and-Peripherals
For the troubleshooting steps, please see below:
First of all, please clarify if the issue is happening only with USBpre2 or if this is happening with any other audio interface connected and set as Playback Engine.
Secondly, please install ASIO4ALL from asio4all.com, set it as Playback Engine and route the signal through USBpre2.
See if the latency persists on the same level.
If the issue is still there, please complete the optimization process. This is highly recommended and can resolve many issues:
http://avid.force.com/pkb/articles/en_US/troubleshooting/en367983
Also, rebuild Pro Tools preferences:
Mac:
1. With Finder as the active application, click on the Go menu, hold the Option key and click Library.
2. Click on the Preferences folder and move the following items to a separate folder on desktop:
• Preferences > Avid > Pro Tools
• com.avid.ProTools.plist
Win:
Go to C:Users > *Your User Name* > AppData > Roaming > Avid and delete the Pro Tools folder. Then, restart your computer.
• Note: If you cannot find the AppData folder, click on the View tab, above Show/hide check Hidden Items.
So, worse than useless. We are on our own I'm afraid. I find ASIO4ALL to be a bit of a dogs dinner, but will try and try again until I can get my head around it, then report back.