Help me for a bass!!!

Hi,
I Have 2 FBT Jolly 8ra speakers www.fbt.it/intranet/Italiano/pae/Diffuso...Jolly-8R-A/index.asp and a Voice System SB 8 subwoofer www.viscount.it/ita/products.asp?id=0B81...11DE822C000393C807AC .
I need a sub for outdoors and i think the MTH-30 is perfect.
What's the SPL could i have with this project???
Is OK (sorry for the bad english i'm italian) for my audio system??
Please answer to my question...

P.S.: My System

Please, be patient Geko. GiveorTake is asking to the mth-30 designer.
However to me a good option could be the punisher, so tested in many setup but pretty difficult to built. An easy and reliable option could be a a 15" reflex tuned at 50-60 hz. How do you cross your 8" midtop? I mean the low crossover point.

At 120Hz.