Hi! This thread helped me out with my Next1, wow, thanks all!
I have worked on the video/audio sync issue and here is my solution you may want to try.
Firmware: v2.1.3
Handbreak .9.5
Only these settings were changed:
Container: MKV File
Under the Video Tab:
Video Codec: MPEG-4
Frame rate: 15
QP: 9
Under the Audio Tab:
Bitrate: 64
Important Note: After the conversion change the file name to end in .avi in order for Next1 to accept the format.