I finally finished adding the Pinwoofer sub and amp to my Met Premium and then later added the BB amp kit (super kit). Here is may full take on experience. First I have to say that Dan has been amazing in his willingness to assist in anyway possible. Just a great experience from a customer service standpoint.
For the speaker system. I added the Woofer kit first. The system is extremely powerful as a sub by itself. I'm not an audio guy (at all) so I can't speak for the technical details with any authority, but the sub kit by itself was like throwing an angry beast inside the cabinet. I had trouble taming it, though I did eventually through some adjustments. I had to first remove the grate, as it was pounding the cheap plastic so hard, it sounding like something was going to shatter. I eventually turned the bass almost all the way down and the game audio to max. I like playing my games loud, but I found the bass was overpowering the Stern BB speakers and that was the only way to find balance. This was an nice addition by itself, but I wanted more.
After adding the BB amp kit...perfect! I can hear sounds that I never noticed before with the stock setup. Super clear and rich audio that you can crank up as loud as you can handle with out losing anything. Having the ability to adjust the BB amp and cabinet bass independently makes a huge difference. This is how a metal themed pin should ship from the factory. I'll say its the best mod I've installed so far, aside from the shaker, which are both must haves for this game.
If you're on the fence regarding purchasing the Pinwoofer kits, my advice is go for it, you'll be happy you did for a game like Met.