If you have a line conditioner, does noise matter?

Most of the conditioners attemp to "filter" some of the line noise, but not regulate the voltage (except for limiting spikes and surges). Dopogue is correct in that your friend would want a regenerator to control the voltage and truly isolate his system from the grid.

While is doesn't adjust line voltage, a sub category of power conditioner includes an Isolation Transformer.
My PanaMax has all the usual power conditioner claims but also has a 400va iso trans. Into this, goes all my low power and digital equipment.
If I could have found the Furman Elizabeth refs, I may have gone that way. As it turned out, the Panamax was available. Not inexpensive, either.

Many, if not most, amps DO NOT like power conditioners. My experience has been mixed. My Rotel RB-1070 really hated the conditioner. My ancient Carver cube? Seemed good with it.
My PSAudio ICE integrated likes it too, but has its own circuit and Solosist outlet.

When it comes to noise reduction , Shunyada is king .

Next to power regeneration, IMO balanced power is the best bet. The technology is proven to significantly reduce power line noise. I've been using balanced power for the past 6 1/2 years. Unless there are wide fluctuations outside normal voltage range and/or brownouts, IMO voltage regulation is not needed.