it's not surprising that you reaped this much benefit from an isolation xformer. Like you said it's results are often YMMV. If you have a lot of grunge on your AC line & you do not have sufficient common-mode rejection then installing an isolation xformer will get you great results 'cuz one thing that an isolation xformer does is provide something like 100dB, 120dB, 140dB of common-mode rejection. They also break-up ground loops (since the pri & sec are isolated with mu-metal casing around each). So, it's no surprise that your noise floor dropped & various textures of the music came popping out!
enjoy the music. :)
P.S. if I may ask, where do you live? your username info says USA. where ever you live, your power is pretty dirty...
enjoy the music. :)
P.S. if I may ask, where do you live? your username info says USA. where ever you live, your power is pretty dirty...