Migration Assistant problems

I have an iMac bought in 2011 and have just bought a Mac Mini. Only a small portion of my photos and music have migrated - how do I transfer ALL my photos and music?

You will need to provide a huge amount more detail on this, not limited to but including the specific iMac model, the specific Mac mini model, the OS versions on each machine, and EXACTLY how you proceeded in doing this.

Ok - will get more info and post again. Thanks for replying.

Migrating from iMac 21.5" mid 2011, 2.5 ghz Intel core i5, serial number C17GG36SDHJF, OS X Yosemite version 10.10.1 to Mac mini (late 2014), 2.6 ghz Intel core i5, serial number C07NL8K5G1HW OS X Yosemite version 10.10.1. Used migration assistant, checked all boxes for data to migrate, hardly any of My Documents have transferred, 900'odd photos out of 2900 and 936 songs out of 4533 . These seems to be iTunes match and icloud stored docs and photos.