filter set-up

Question
Hello,I just bought a used 90 gallon tank yesterday.The question I have is the tank has an overflow in it.It Has the black casing and 2 holes in the bottom of the tank.Its going to be a freshwater tank.I have 2 Oscars and 2 jack dempsies.I'm not sure if I should use that kind of filtration system or would it be better to somehow plug up the holes and use a regular more common filter system on the top of the tank.I dont want to make a mistake. I could really use some advise.  Thanks

Answer
I asked around for you and got this site, which seems very helpful.  I have never had the opportunity to run anything larger then 55g as I live in an apartment.
http://www.reefland.com/rho/2006/05/overflows_sumps.php
I hope this helps answer your question.