To make the above comment more complete, a power conditioner won't change how your system sounds at all. If one is needed, all it will do is make the input ac of your system more stable, but there are internal circuits that convert the input to dc, then to ac through a chopper circuit, which outputs a higher hz ac for use with a smaller transformer. However, during the dc stage the power supply can be used to deal with most fluctuations, as such, most fluctuations get filtered before the dc is converted back to ac, giving the system better ac to use than the input ac. Simply adding a power conditioner will only make the input ac more clean, though, unless you were experiencing fluctuations so great that the device was having trouble operating, i don't think you would need a power conditioner.
However, ignoring that, a power conditioner cannot affect the output audio of the amp, let alone its frequency response, which is modulated by the input signal.