Is this an assumption from reading forum threads or have you been involved in tested multiple systems with poor grounds that have been improved upon and now have a very low resistance high performance ground? (...)
Mostly by long experience with XLR equipment from sellers such as VTL, Audio Research or Atmasphere, and experience with SE electronics, such as Lamm or conrad johnson. I found that quality of ground affects - or even not using it - affects very little the balanced brands I referred,
but was discernible in the non balanced systems.
Technically, connection to ground only affects safety in properly designed and connected equipment. But we know that properly designed and connected equipment is something that is almost non existent in high-end audiophile systems ...
My listening room has a decent ground connection - when I wanted to emulate a poor one I just added a 22 or 47 ohm resistor in series.