ive seen a few people talk about moding them, but the actual filtration doesnt do too much IMO. with enough live rock it doesnt matter which way the water is going in your filtration or anything. i dont know if i am seen any saying it doesnt work though...
but IMO, the biocube is ahead of the eclipse because it looks nicer, it has lighting so you can maintain a reef. also, they do make skimmers for a biocube. im not sure how well they work, but depending on the brand, i have heard that some of them are okay. the only skimmer an eclipse could hold is on that can go in your tank, which severly limites your options also. you are limited (as far as i can think of) to a crappy one like a Lee's for a visajet (i dont believe that owuld fit though...) or a deltec MCE 500 or 600, not sure if youa re wanting to spend that much money though.... im sure others will have opinions too, but that is mine. also, with the eclipse, you will have to upgrade lighting because it oesnt have the lighting needed for a reef. you can then do a retrofit, or you would have to replace the top entirely which would mean youd have to replace the filtration as well.