Ubglub: Neither the P3 nor the EP15A use iso-trannies for outlet/component isolation. The P3 has more (and, it would appear, more extensively) isolated outlets than does the 15A when used by itself, but both units use filters for that purpose, not iso-trannies. The Shunyatas, in common with most PLCs, are passive units that aren't transformer-based, so they can't regulate voltage or provide balanced AC (of course Shunyata would argue for the superiority of their approach based on other reasons).
The API Power Wedge Ultra 116 I use after my EP15A has six individual iso-trannies for source components and preamp, each individually selectable for balanced, floating, or regular operation. In my system balanced is almost always best sonically (but never worse) for each attached device as compared with the other settings, so I believe I can vouch for the general efficacy of balanced AC (which the P3 provides by itself). But there's no meaningful way I can make a comparison of whether the individualized level of inter-component isolation I'm getting is more beneficial than a lesser degree of isolation would be, without also introducing uncontrolled variables which would invalidate the test, though one assumes it couldn't hurt as such -- the possible exception being if the iso-trannies were in and of themselves inferior-sounding to another, filter-based approach (something I can't answer, other than to say that using the PWU results in better sound than just plugging my sources straight into the EP along with my power amp, *even if* balanced AC isn't selected on the PWU).