What do you mean by 'automix'?
Why not create a playlist and then set it to play? If you use a Mac version of iTunes (not sure about PC or ios 8 versions) you can go into settings and turn on crossfade and set the number of seconds to do it for. That will give you gapless playback.
If you have an iTunes store account you can log in through iTunes and then turn on the Genius playlist feature which will supposedly automatically select songs that are similar to one you select and create a playlist of those songs. Never actually used it myself.
Genius
The Genius feature, introduced in iTunes 8, automatically generates a playlist of songs from the user's library which are similar to the selected song. Genius playlists are created by the ratings system and collaborative filtering. An iTunes Store account is required because information about the user's library must first be sent anonymously to Apple's database. Algorithms determine which songs to play based on other users' libraries, and Genius becomes more intelligent given a larger data set. The resulting Genius playlist can contain 25, 50, 75, or 100 songs and can be refreshed for new results or saved. Once Genius becomes active in iTunes, it can be used on current generations of the iPod Classic, iPod Nano, iPod Touch or the iPhone.[35] iTunes 9 added Genius Mixes, where the Genius software finds similar music and automatically puts them into mixes.[36] iTunes Genius creates playlists from the user's existing iTunes library based on a single selected song. Genius Mixes create playlists based on the musical genre.
My other Honda runs on grass.....cuts it too.