This scanner dates from before Apple switched to Intel processors, and long before Apple dropped support in OS X 10.6 and up for PowerPC applications.
Your 27" iMac has an intel processor, and as you say it is "brand new" it is probably running OS X 10.8, which can not run the old software.
Your best bet is to go to Epson's site, and download the latest software they have, or find out what they may suggest.
