Filter socks are generally easy to reach and change out. Floss in the bottom of the sump will require you to dunk your whole arm in. Also, rinsing the socks out or throwing them in the washing machine is pretty easy. That foam you speak of will eventually stop water from passing through it if you skip maintenance...filter socks simply overflow.
the sock will stop detritus before it hits the sump. Your floss idea will allow the first chamber to get pretty dirty and need cleaning regularly.