ok... Seeing how you're very limited in space (in terms of fitting a sump in the cabinet,) I would scrap that idea, still not spend the money on an eheim, and possibly go with a hang on back model refugium.
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+3727+3618&pcatid=3618
Check out this thread. Only thing, since the tank is a hex. you'd have to make sure something like this would fit...
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+3727+3618&pcatid=3618
http://www.aquariacentral.com/forums/showthread.php?t=213672
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+3727+3618&pcatid=3618
Check out this thread. Only thing, since the tank is a hex. you'd have to make sure something like this would fit...
http://www.drsfostersmith.com/product/prod_display.cfm?c=3578+3727+3618&pcatid=3618
http://www.aquariacentral.com/forums/showthread.php?t=213672