This or that manufacturer says all filtering is bad. That is THEIR subjective opinion. There are bad filters and there are good ones. Listen to a number of different products for yourself and form your own opinion. Filtering in some surge protection devices is simply a noise suppression cap across the hot and neutral. You can easily cut the leads and remove these if necessary.
Surge protectors without noise rejection
Is there such thing as a duplex outlet or power strip surge protector, that won't alter sound because of built in noise filtering with surge? Seems there is filtering with surge only protectors. Even Brickwall seems to have some sort of filtering...is this inherent with surge devices?