I can't believe this much time as passed. A "few" years ago, I built a pair of Madisound's BK-16 back loaded horn hits and dropped some Fostex FE168EZ drivers them in. You can read about it here: https://www.superbestaudiofriends.org/index.php?threads/set-and-fostex-blh-speakers.1358/ What I wanted to do next was build out the Frugel-Horns, the XL version that would fit the larger 6" drivers. I'm years late. There are some differences between the FHXL and BK-16. The Frugel-horns have the horn exit towards the back, are of an arguably simpler design, and have a longer section behind the driver with a choke near the exit flare. With respect to use, I gravitated toward the Frugel-Horn because it was designed to be used against the wall, instead of needing to pull them several feet from the walls. The BK-16, especially with the 168ES I sound to be midbassy and murky if not placed at least one to two feet from the wall. Not so with the FHXL where I had them placed against the the wall angled in a bit. The drivers most often recommended with the FHXL are the Mark Audio Alpair. I had used the Alpair 10P before and didn't like them. I gave them away or sold them for cheap to a SBAF member. The 10P did a lot of things right, they sounded smooth with respect to frequency response; however, they didn't resolve enough information, lacked immediacy and liveliness, and needed more power than what SET and many PP tube amps could provide. Maybe one day I will try the latest and greatest TOTL Mark Audio MAOP drivers, or maybe not because I don't think I necessarily want to drop solid-state True HiFi capable monoblocks into the mix. I already have too much crap in the house. Anyway, I've had always had success with Fostex, particularly their higher-end drivers, so why not? I ended up with the fairly new FE168NS (not ES) but accident because I didn't look carefully while I was on shopping Madisound's site. Oh well, but it turned out to be a happy accident. The NS are based on the limited edition SOL series. I have kept away from Fostex's limited edition series because I never know when one of my kids is going to poke a hole through a driver (boy and girl, but they fight like cats and know stuff over). The last thing I wanted to worry about was to be stuck with one expensive driver with no possibility of replacing the other. This is how I've set them up. @Boops: for the record, I decided on the EC Custom 45 for amplification. The PP Fisher amp very worked well, more heft, warmer tone, and takes the edge off the highs more. Ultimately the Custom 45 was more musical, spacious, and honest. Sometimes honesty may be too much for wide-banders's frequency response nonlinearities in the highs. I swapped out the neutral sounding DAC for the dark sounding DAC, the Yggdrasil LIM to obtain the best synergy. Having be running BWC "big woofer club" speakers for a while, the first thing I noticed on the FHXL was mid and high bass not being anywhere what I was used to. However, everyone in the family agreed that somehow these diminutive drivers, through the clever science of leveraging the backwave to augment the low frequencies, offered a certain musicality that the JBL4698b were not capable. They also look much better in the living room, so I guess these are staying. The FHXL with the 168NS doesn't seem to be quite as punchy or snappy as the BK-16 cab with the 168ESs. On the other hand, the bass seems to extend more effortlessly, and there appears to be a lot more latitude for adjustment via placement of the speakers and internal acoustic stuffing. I have small weights over the top lid to get a good seal while I still tweak things. I'll glue the top in once I feel comfortable that I have gotten things right. Obviously there are limits. They aren't going to be able to blow out your ears, and do it cleanly without distortion, like these. AC/DC at 100-110db effortlessly just ain't gonna happen. These are better for girl + guitarist, jazz, sparse electronic, chamber orchestra, and solo.