Ok maybe I can shed some light on this subject, I've been researching monitors and the best ones almost always use torroidal transformers, in fact the first three from the list use torroid transformers the rest as far as I know use regular EI transformers. Usually only higher end monitors like genelecs and dynudios use them because torroids are more expensive, only a few monitors under 500 use them which I will list below. The audioengines and swans are overated IMO, not that they are bad and these also use torroid transformers, but they use passive crossovers to separate the highs from the lows and use one amp to power both speakers. Active speakers use active crossovers which don't suck clarity from sound like passive ones do and each speaker has its own amp and power supply, as some of you may know in audio getting good clean power and good power distribution is like 50% of the battle to getting good sound. By design an active speaker is always going to sound better.
These are the top 4 best sounding monitors IMO under 500 in ranking order these all use torroid transformers as well.
JBL 2325p
Tapco S5 ( identical to MR5's)
Mackie MR5
BX5a