I believe LF is referring L
I can't speak for skally or Cel4145 but I'll try to explain it for you. Over 30Hz, the PA-150 will have the ability to play louder. 30hz is fairly low and will make your picture frame vibrate depending on how loud your volume is of course. But when movie contents sends signals under 30Hz, the PA will still play them, but the volume (output) will start to decrease as the "sound waves" gets lower (lower Hz) until it doesn't have the ability to play them anymore which is around 25Hz.
The Outlaw, will still play very loud but not as loud over app. 30Hz because the PA a bigger driver. BUT the Outlaw has a better driver. When playing content under 30Hz, it's volume will decrease a lot less faster then the PA. Also, it will play content (extend) below 25Hz (very deep bass). As a matter of fact, it will play all the way down to 20Hz.
At reference level, you may not find the very deep bass (20Hz) to be "loud" but you will feel it. You feel it in your skin, your chest, your couch...it's just plain fun.
More and more movies are including sub 25Hz content in their audio track so that's why most ppl will strongly recommend subs like the Outlaw. When you watch your favorite Transformers or War of the World, you will smile uncontrollably and never look back
When Skally and Cel chimes back in, they probably will give you a better explanation as their technical background are greater then mine but in the meantime, I hope it help you understand a little better.
Edit: kini and cel already beat me to it