wow that brings back memories...I would have never guessed they still made these. They were one of the original "subs in the trunk". Put out a lot of sound for the size/cost but not the tightest bass. I remember mine being pretty impressive for electronic muisic/rap but then the first time I tried a little AC/DC was really disappointed.
If you push it below port tuning, you could blow the driver unless it has some type of built in passive crossover (capacitor in line?).
You might try plugging the port, it would allow it to play lower without driver damage but of course would cut output up higher.