Khornukopia

They should have used different numbers too, not just change one letter between two similar looking parts.

That is what the manufacturer's spec sheet lists, but I would not guess it is that narrow when I listen to them. The sound seems to "project" out into the space in front of the speakers.

Selenium made the HM-4750 90x60 with the narrow throat, and the HL-4750 40x20 long throw. The ZXPC 17" X 11" looks like the HL-4750, but is made of ABS type plastic.

Polyimide is an excellent choice for a tweeter diaphragm because of its strong, lightweight physical properties. I bet your new La Scala AL-5s sound as good as they look in your room.

I have a pair of the 17 X 11 and a pair of the 18 X 10 on speakers in the same room. I like them both. The 18 X 10 is a more "normal" dispersion design (shallow version?) and therefore better suited for the average listening room. I also find the 18 X 10 to be more attractive. If you plan to make grills, the 18 X will be easier to cover, because of the lip on the 17 X.

The eBay listing does not have specs, but the horn appears to be a clone of the Selenium HL-4750.

I wondered about your polarity earlier, but the way you further describe the condition, it is most likely a room mode bass null at your listening position. I suggest you start by placing the speakers up on tables or chairs and listening with Audyssey turned OFF.

I think many other forum members would also have suggested the same thing earlier with more of the details upfront. Bass null problems are sometimes difficult to express and understand.

Have not done anything different with my stereo recently. Sometimes I like to go out to places where I just hear a soft breeze through the leaves, or some birds chirping.

You have standing waves that are cancelling the bass. You need to change something about the relationship between the speakers and the shape of the room.

The smaller nearfield speakers may have more distortion at the same comparable output level, therefore will be annoying to the people in the other rooms. The output from the rear firing port aimed at the wall is usually not good for people trying to fall asleep in the next room.

Low cost wires are always a weak link and prime suspects. Then you involve laptop hardware and the various software programs with very complex structures, where the slightest interface glitch for a single command can cause headaches. Combine those and create some puzzling outputs. Glad you fixed yours.

Have you verified that the speaker wire polarity is correct, all the way to both woofers?

Have you tried a different connector cable?