Balanced vs RCA between amp/preamp

@atmasphere 

" The problem with this approach" Do you mean Transformer coupled approach?

As far as I know transformer coupled way is to solve the ground loop.

That's the reason we use the transformer isolation instead of RCA to XLR cable,right?

The way to solve a ground loop is to purchase properly or fix improperly designed equipment. Adding a transformer is a bandaid. Bandaids fall off.

My company wired recording and film studios in Los Angeles and New York in the 1980s & 1990s. We had transformer and electronic balanced and unbalanced equipment to interface. Hundreds of connections that could be reconfigured into literally millions of combinations. Correctly done, there is no ground loop.

If you detail out your equipment and connections, perhaps we can solve your issue. By detail, I mean brand, connection, electrical power etc. Since we can now post images, draw a sketch.

" The problem with this approach" Do you mean Transformer coupled approach?

@runwell No. If you are dealing with a ground loop, the transformer can fix that, but take @ieales' post seriously.

My Ayre electronics sound better using the differentially balanced outputs/inputs than the RCA's

@atmasphere 

 You suggest to use transformer isolation and you deny the way to use it. 

What is your opinion?

Audio Research reply directly that I should use transformer coupled  to connect RCA pre with their XLR only power amplifier.