Create /usr/local/src/SoX directory, download, extract sox from sources:

#mkdir /usr/local/src/SoX
#cd /usr/local/src/SoX/
#wget http://softlayer-dal.dl.sourceforge.net/project/sox/sox/14.4.2/sox-14.4.2.tar.gz
#tar xvfz sox-14.4.2.tar.gz
#cd sox-14.4.2
#./configure

After running ./configure you should see in output:

OPTIONAL FILE FORMATS
amrnb.....................no
amrwb.....................no
flac......................yes
gsm.......................yes (in-tree)
lpc10.....................yes (in-tree)"