From ASRock's site, the User Manual for the motherboard states
"This mother-board also provides independent display controllers for DVI-D, D-Sub and HDMI to support dual VGA output so that DVI-D, D-sub and HDMI can drive same or different display contents."ftp://22.214.171.124/manual/Z77M.pdf
It only specifically mentions dual monitors. It makes no mention of three monitors.
Intel's, Question search has this to say
"Most Intel graphics products can output to one or two displays at the same time and support several different multiple display configurations.
Starting with the 3rd Generation Intel® Core™ Processors with Intel® HD Graphics 4000/2500, three displays support may be possible depending on your computer's configuration. Check with your computer manufacturer if three displays are supported on your computer and which display combinations are supported."http://www.intel.com/support/graphics/sb/CS-031040.htm#3
I emailed ASRock's support, and posted to the Intel forum.