Mr. Penngotti,
You and I are kindred spirits. I also like the music loud with a good thump from the kick drum. The good news is that it is doable. The bad news is that it is not quite as simple as just adding a subwoofer, though that is a good start.
In my opinion you do not need to buy expensive subs. I like the SVS SB4000. I also like Rythmik, but they don’t do loud as well as the SVS.
Regardless of what brand you end up liking, multiple subs will help minimize a lot of the room acoustic issues you could run into when you introduce powerful low end into your system.
Liking it loud with a strong low end will more than likely cause you to push your system too it’s limits so I would also be looking at subs (as well as all of your gear) that have actual balanced inputs. If you really want to achieve arena levels, you will need every bit of gain you can find and having a balanced system really helps with that.
Down the road I would look into some type speaker management system to limit the band width that your Snappers need to reproduce so they don’t get eaten alive trying to drive those Harbeths full range.
You can pm me if you have questions.