I use an MIT passive filter in the form of the "Z-Strip" and I noticed a rather obvious improvement in noise floor reduction. I recommend it based on several experiments where I would add it and then remove it to see the difference. It works consistently with everything. But I haven't tried any others so.... My audio buddies use the PS Audio Ultimate Outlets and got similar results.
My reservation about power regenerators is that many times, more noise comes from the stereo components than the incoming power. I have seen this MANY times testing electronic equipment in my lab. You can even see the results that the rat's nest of cables can bring on - by jiggling the cables, you can see the noise level change on an oscilloscope. It is interesting and scary at the same time. A regenerator won't make a bit of difference here since the noise is injected downstream of it.
However, it is unclear as to whether your problem is the incoming power or your amps. At very high gain, everything is amplified and there is no way to know what is the cause without experimenting. If the regenerator lowers your noise floor, then the problem was your power. If not, it is your amps. I am inclined to believe it is the residual noise floor of your amps you are hearing.
Since the noise isn't really coming from your tweeter, I suspect you may be hearing spurious noise from your power supply in 60 and/or 120Hz form. Only that frequency range would be audible from your woofers and mids. The noise I was talking about before is much higher in frequency and so is only heard in the tweeter. I don't think any regenerator is going to solve this problem but passive filtering might. Let us know what you find out!
Arthur
