Floating ground in the apt. Building

Hello

i live in a common NYC postwar apt.building (270 units)

i changed several during my life in NYC and was always floating ground on the breaker side. Connecting the ground always resulted in the system being dark, bassy, constricted. Lifting the ground always brought back the air and widened the soundstage. The building I currently live in had the crappiest breaker panel I have ever encountered so I decided to connect the ground just in case. The ground wire in my cryo’d romex spool was cut shorter from not being used and I needed a jumper of sorts to connect it to the ground terminal. I didn’t have any 10 gauge wire on hand so I temporarily used a 5 inch piece of regular extension cord. The sound became fuller in the midbass region but did not lose any air. Now I went out and bought a piece of 10 gauge romex and after connecting it the soundstage collapsed and the sound became dull again. I reconnected the cheap multi strand piece of extension cord and everything is nice again.
I have 2 questions:

1. I heard or read somewhere that you don’t have to ground equipment in big apt. buildings since they are already grounded. All existing outlets on other breaker lines in my apt. are 3 prong but do not have a grounding wire running attached to them.
2. Have anybody experimented with different gauges and materials like silver when it comes to grounding? In my case, the cheap extension cord piece is a clear winner over 10 awg Romex but it left me curious of what else is out there I can try.
sorry if my post is kinda jumbled and confusing.
any feedback and experiences would be appreciated.