Finally was able to use my 618s XLF this past weekend. I used them while running sound for a rock band and for dance music between sets. The tops I use are JBL PRX 525.
I bought these to replace my PRX 718s. Mainly because I want a total of 4 subs but the 718s are discontinued and I like to have everything match. (I know..picky me)
Out of the box quality looks to be about the same as the older PRX line. The rear amp and controls are near identical. One difference is the top is not flat, its concaved in the middle. Probably to match up with setting the mains on top. Not sure if this will be a problem in the future or not while running 2 per side. Another difference is it does not have the lighted JBL on the front. It now has just a small blue light like QSC powered speakers. I kinda liked the lighted JBL. Oh, and it takes a screw-in for pole mount speakers. Sooo, that means I need to buy new poles....damn. One other think I noticed while carrying these is that they may be a little bit front heavy. Could just be the way we carried them but it did seem so.
While I haven't done an A/B with the PRX718 I think the output is very simular. While the band was playing the kick drum came through loud and clear with a nice thump. I pushed them pretty good and never got any distortion or clipping. Running the Ipod between sets sounded amazing. The bass was like thunder on the dance tunes. If you are real serious about your low end don't waste your money on the 618s, get the XLF. It may cost a couple hundred more but its worth it.
If I can, I'll do an A/B with the 718 this week.