Empire Grenadier 8000P

I would like to tap into the arsenal of knowledge on Audiogon and ask a question about the Empire Grenadier 8000P's. It involves something that has always confused me. On the back of the cabinet, there are 6 small ports. I've seen 8000P's with all sorts of configurations with regards to these ports. Some have all six ports plugged with a small plastic cap. Others have them all open and still others have every other combination of them plugged and un-plugged. Since I did not buy these new and have never seen an owners manual or any explanation for these ports, does anyone know what they are for and how or why you would use them, plugged versus un-plugged? Are they to be all removed, all installed or some combination based on speaker placement? Feedback would be appreciated. Thanks!