FLAASH always outputs scaled integers to reduce the file size.  The scale factor used is in specified in the advanced settings and its default value is 10,000.  So you can divide your data by this scale factor to get to reflectance between 0-1 (and sometimes higher or negative for poorly modelled pixels).  Note that storing your data as floating point values will double the size since it takes 4 bytes to store a float value compared to 2 bytes to store the integer value.  If you have a full size Quickbird image, it can make the reflectance cube very large.