Isolated ground for 20 amp

Hello,

I am planning to have three 20 amp circuits run from my panels into my music room which is right next to the basement where I got two 200 amp breaker boxes. 

To add an separate breaker box directly from the transformer, I was told it would be very expensive and it would make it commercial.

The electrician said, he can make a separate 100 amp panel and run 3 20 amp circuits. But the ground from the separated breaker box will be connected to the ground of one of the main panels. If the grounds are finally connected to the main panel, what is the point of having a separate 100 amp panel? I have quite a few 20 amp slots available in the main panels.

I am also reading about isolated ground. What does it exactly mean? I also read that, it is dangerous to have isolated ground and regular ground next to each other, as each can have a different potential and it can kill people when touched simultaneously.

I also read that, all grounds have to be connected to each other as a safety code. If that is the case, how does isolated ground actually isolate?

Also, I want to connect my components directly to the three 20 amp lines, so I can save cost on conditioners. How do conditioners work? some say they impair sound.

My components are: Reed Muse 3c, Ypsilon MC26L SUT, Ypsilon VPS100, Cary SLP05, Cary DMS600, Cary CAD 211FE monoblocks, KEF Blades

Sorry, any guidance is hugely appreciated.