The output of a power conditioner is going to still be a sine wave, so you're not departing from the domain of AC. They can be a bit helpful for reducing the potential for ground loop problems, plus they generally offer some decent surge protection. You do have to make sure that a power conditioner or surge protector does not limit the current output, mainly for the sake of power amps that have varying and often very high current demands (source components need comparatively little current) - this is probably the concern that you've heard about before, but many home theater power conditioners (such as those from Panamax, Belkin PureAV, and Monster) include a set of "high current" outlets specifically intended for supporting amps and powered subs.