I use an API Power Wedge Ultra 116 with my front end stuff (it follows an ExactPower EP-15 used for waveform/voltage correction). The PWU provides separate center-tapped isolation transformers for each of its 6 outlets, with switches that allow you to choose between normal, floating, and balanced power options for each attached component. (This unit cannot provide balanced power to power amplifiers, so I haven't been able to test that application.)
Therefore, the PWU provides a reliable test for how each piece of gear reacts to balanced AC on an individual basis, without throwing in confounding variables. To date I've only used one component that showed no improvement from selecting balanced AC (an older Conrad-Johnson tube preamp), and that one showed no degradation either. All other components tried, primarily SS preamps and digital separates (my phonostage is battery-powered, so it doesn't apply here), showed varying degrees of improvement, from very slight to pretty vast as far as these things go, but again never any degradation. (All these pieces also sounded better fed from the PWU than they did skipping it altogether, no matter which switch position was chosen, so the powerline filtration it includes in addition to the iso trannies would seem to be doing no harm here.)
Based on this evidence, I'd say that balanced AC done properly (independent of any other filters or such that might be included in whatever device is balancing your AC) probably rarely has any downside used for line-level components such as sources and most preamps. If there's a problem with a power or integrated amplifier, I'd investigate whether it could be due to inadequate iso tranny capacity. The issue may have more to do with undesired raising of the powerline impedance seen by power amps than balanced AC per se.
Therefore, the PWU provides a reliable test for how each piece of gear reacts to balanced AC on an individual basis, without throwing in confounding variables. To date I've only used one component that showed no improvement from selecting balanced AC (an older Conrad-Johnson tube preamp), and that one showed no degradation either. All other components tried, primarily SS preamps and digital separates (my phonostage is battery-powered, so it doesn't apply here), showed varying degrees of improvement, from very slight to pretty vast as far as these things go, but again never any degradation. (All these pieces also sounded better fed from the PWU than they did skipping it altogether, no matter which switch position was chosen, so the powerline filtration it includes in addition to the iso trannies would seem to be doing no harm here.)
Based on this evidence, I'd say that balanced AC done properly (independent of any other filters or such that might be included in whatever device is balancing your AC) probably rarely has any downside used for line-level components such as sources and most preamps. If there's a problem with a power or integrated amplifier, I'd investigate whether it could be due to inadequate iso tranny capacity. The issue may have more to do with undesired raising of the powerline impedance seen by power amps than balanced AC per se.