How to copy files from tablet to PC - Not all files show up in PC

When I connect my Xoom to my PC via USB cable I get a Xoom "Portable Media Player" showing up in my Windows Explorer. When I browse the drive, I can only see half the folders compared to if I browse the SD card directly from within Astro file manager on the Xoom. Why aren't all files and folders showing up? In Android (3.2), I've tried copying a file from a "hidden" folder to a folder that I can actually see on the PC but the file does not show up. Someone suggested it was because it didn't get mounted as "USB Mass Storage". How can I copy the files? (same functionality works fine from my HTC Desire)