The DMG I found here installed Mix v1.0.1 as well.
On the Mix releases page, we see that version 1.0.1 was released on February 17, 2016.
On the Solidity releases page we see that Solidity v0.2.2 was also released on February 17, 2016.
As of April 19, 2016
Solidity is Version 0.3.2 and
Mix is Version 1.0.3.
It seems like that disk image is out of date.
You could try installing via Homebrew using
brew tap ethereum/ethereum
brew install cpp-ethereum --with-gui
brew linkapps cpp-ethereum
I tried but it took too long (I stopped after an hour or so) and I needed to get real work done. The warning on the Homebrew page is no joke:
that brew install on El Capitan machines triggers a (very slow) build from source.
Unfortunately, it does seem like your best option is to build from source at this point.