Feedback is caused by a microphone hearing the speaker it is playng through. If there are peaks in the response of the speaker or room then feedback will occur at those frequencies. Distortion has nothing to do with it.
If you notch those frequencies then feedback will be reduced, not avoided. The feedback will probably simply occur at another frequency.
A notch filter should have a fairly high Q (a narrow response) so it doesn't reduce too much of the program. Then it must be accurately tuned, not just guessed.
Can't you borrow or rent an adjustable notch filter to see its small effect on feedback?
If it works then you can make a real notch filter, not a bunch of bandpass filters.