Contacting Pioneer would be your best bet.
I suggest you try setting a conversion rule to convert MP3 to MP3. You may want to experiment with conversion to CBR (set in MP3 Conversion rules).
- The Pioneer may be tripping over some tag, see if Amazon MP3's have some tag that CD ripped MP3's don't. Then experiment with removing these tags from some sample files that failed to show on the device and see if it worked.
- Most devices would support VBR encoded MP3's but you can try forcing CBR encoding by setting conversion rules.
- It would be strange, but try a lower bitrate for MP3's.
I would try to remove all, but Artist, Title, Album, Date, Track# and Album Artist tags from files and set to convert them to CBR 128kbps. Then sync some files that failed to show before and see if they show now.
Lowlander (MediaMonkey user since 2003)