Audiophiles start nit picking before the foundations are right. EMI/RFI testing is fine, but we don't hear up there, and bigger AC issues may be lurking.
Start with a simple meter like this one on the output of your conditioner. Make sure the LED lights on top light up correctly, and if so then watch the voltage over time, including neutral voltage.
How much does it drop when your stereo is on or plays? Morning much better than evening?
This will help you gauge whether you need a dedicated line or voltage regulator as a front end. Also make sure you don't have other issues!