I have a similar Isoclean setup as you (3030G & SF cables) and have experienced exactly what you did with the filtering within the Isoclean -- loss of dynamics, bass and soundstage. Therefore, I went with one of their power bars (non-filtered).
I'm not sure how to explain it other than it must take away AC noise & some grunge as I call it & in so doing decays or muffles frequencies (maybe a little grunge is necessary????). I'm unable to explain anything about power cord theory -- so, you're expecting too much if you're looking for a direct answer why.
As far as a Duet -- I have one, tried it and it did nothing for me -- so instead of selling it, I relegated it to the flat screen and DirecTV receiver.
I'm not sure how to explain it other than it must take away AC noise & some grunge as I call it & in so doing decays or muffles frequencies (maybe a little grunge is necessary????). I'm unable to explain anything about power cord theory -- so, you're expecting too much if you're looking for a direct answer why.
As far as a Duet -- I have one, tried it and it did nothing for me -- so instead of selling it, I relegated it to the flat screen and DirecTV receiver.