Markers are really meant for line graphs. There you can have lots of markers, even between values.
Markers work by you specifying the point # or a fraction between it. Below you see
group2markers="0.5,0.6,0.7,1,2,3"
This means on the line for group 2, place a marker 50% between point 0 and point 1 (and one at 60,70), then place a marker on point 1, point2, and point 3.
[easychart type="line" height="100" title="SYSMark 2007: AMD v.s. Intel" groupnames="AMD Phenom X4 9950, Intel Core i7 940" groupcolors="005599,229944" valuenames="Overall,E-Learning,Video Creation,Productivity,3D" group1values="157,132,208,150,148" group2values="229,202,259,226,232.43" watermark="100,150" currency="$" precision="2" group2markers="0.5,0.6,0.7,1,2,3" ]