I love Viking, but in my opinion they really did an injustice by promoting a system that can drive a large number of 8 ohm speakers. As you are seeing, you don't have the ability to control the volume of individual speakers and that is an important consideration in most installations. The "tried and true" solution is a 70V system. The speakers have transformers on them with taps that you use to change the volume. The speakers get wired the same way as you have now and you actually can use much smaller gauge wire. They also can't be much more than a dollar or two more in cost. That PA30 has a 70V output, so why does Viking even suggest a bunch of 8 ohm speakers?? I don't get it.
More to your question, absolutely try turning the horn in another direction. I've found paper, packing material, cotton stuffing packed into horns that can (ahem) be quite effective with problems like this.
There are 8 ohm wall mounted volume controls such as this-
https://www.atlasied.com/f/2126/SL4.1570.PDF.pdf That's actually a stereo control, just use one section.
-Hal
