Hi mac, first off, I’d have to say that quite literally it would be an impossibility of physics that any power solution (no matter what it was or who made it) could be so sufficient that no further electrical noise reduction would be audible...that’s because noise (at the quantum level) is random and self-generating - wherever voltage is present, you have noise. For anybody’s method to work, in either direction, downstream or up, the effects of noise reduction fades as physical distance increases. The noise fades the further you go from the source and the noise reduction effect likewise fades the further you go from the noise reduction device. That’s why he makes so many different devices - to attack closest to the noise where it lives, at the various sources of noise in your home (fridge, HVAC, light bulbs or whatever your wanting to tackle). In short, noise is unavoidably all around us, nobody, not even Alan, will ever be able to get rid of All of it. And the reverse is true. Any noise reduction device you buy will make an audible difference. IOW, there is no such thing in this case as a point of diminishing returns. No matter how many noise reduction devices you have, you can always add one more and hear a difference.
But, there is a problem somewhere with your situ. Alan would prefer that a customer buy and Install his products in a particular sequence, at least in the beginning - where the power enters the home in particular. This, for lack of an easy, clear explanation for us here, sort of "guides", "chases" or "channels", if you will, much of the remainder of the bulk of the noise to areas further inside the home where other AMD devices can be installed to squash it most effectively. Buying his products more in a random fashion without this consideration may be the underlying problem here. It may not be that the existing AMD products that you already have are no good, it’s just that the process of the installation of the particular first few AMD products I describe needs to be followed (and quite thoroughly, frankly, since there are a number of points to be aware of, but Alan himself would be the best source on that - he responds quickly and fully to those questions, IME).
If you need more help from me, let me know.
Regards,
John