Yea I know what you mean about the filter socks and the drain tube configuration. The pictures on Aqueon's web site confused me too. The way it works is the drain tube goes into a clear tube with a cap on the lower end of it. This makes for a quieter flow of water (i'm told) into the first chambet of the sump. The water from the tank fills the tube and overflows into the plate that the filter socks sit in. It then flows down through the socks and continues up over the first baffel to the fuge area. I'll try and post some pix. when I get a chance. If you are curious check out Youtube, some guy in NYC has posted some pretty informative videos on this sump, one of the driving forces in my buying it instead of trying to build one.
As far as the DSP in the fuge, I guess you are right 5" of sand would really limit the space in there. I assume you would still go with the LR
along with the macro algae? I thought I might try and get some mangroves going, more to see if I could get them going than anything else.