Step 1 is to determine the source of the buz or noise. Is it a ground loop? Is it a noise generated by an external device like a dimmer or appliance? Is it DC on the line. Ground loops are heard through the speakers or subwoofer & DC is usually heard internally with buzzing transformers. From my experience, line conditioners or isolation transformers will do nothing to filter ground loops or DC on the line. Dedicated lines won't solve the problem either. Ground loops have to be solved at the source or top notch ground loop isolator has to be employed. DC is even more difficult to isolate and treat. Emotiva & iFi make excellent DC filters. I use the Emotiva for DC issue and for the ground loop I use the classic Mondial Magic Box. For a line conditioner, I have a Furman Ref It15 which has an isolation transformer built in and it does nothing to prevent ground loops or treat the DC issues. So my conclusion after a 3 year battle with a DC on AC is no line conditioner will work to prevent those noises and you will need multiple specialised filters in addition to the line conditioner.
