I posted a different thread to get a better understanding of how running speakers in parallel worked. Am considering adding an identical pair of Hawg Wired ZX speakers and running them in parallel with the ones I already have off of the RS400 amp (am thinking of adding lowers for the second pair). These speakers are rated at 90 db sensitivity. Was wondering from those of you that have experience with Hertz or Focal what would be the better improvement all around. Am looking at the HSK 165XL from Hertz thats rated at 93.5 db sensitivity or comparable speakers from Focal. The ZX's retail for for $200 so that would be the cheapest route by far. I've never heard the Hertz in person, just read comments about them on the forum. I've heard the Focals but not just a 2 speaker system on a bike. I know you pay more for higher end pieces of the puzzle, just wondering if I would have a better end result with 4 of the ZX's in parallel or by spending the extra cash on one pair of higher end speakers and replacing the ZX's I currently have.