DC filter

A friend using the Pass Labs X250 power amplifier with a newly made transformer without mechanical hum (the original one buzzed very loudly from 200mV DC in the mains) did some experiments with different DC filters. All filters in the kind of those under
https://www.lcaudio.com/index.php?page=316
don't provide an improvement of sound quality - instead, the dynamic behavior deteriorated, probably due the high DC resistance (ESR) of snap in capacitors.
But the use of a DC-Filter as to find under
http://scintilla-buizenversterkers.nl/scintilla-buizenversterkers/zelfbouw/zelfbouw sites/DC-Blocker.htm
but capacitor values 47.000uF/63V ( 4 pcs., unfortunately not cheap) provide an improvement of sound quality in all respects.
With and without this DC filter version makes no difference regarding the mechanical hum behavior (in both modes extrem low).
It may be that there are harmonics from the DC components from the transformer, that are absent when using the DC filter ?