What do you mean by "power"? I get that you want to play at high SPLs, but if you are going to use bass and high treble supplementation and probably roll off the response of the SL speakers with very steep slopes, given your penchant for digital crossovers, then why do you anticipate needing the transformer to take lots of power? Have you evaluated the specifications of the Plitron toroid, so as to form a basis for your belief they cannot be driven hard, or what? Anyway, I have no compulsion to dissuade you from your aim to use Sowter transformers. (1:100 would be technically more correct than 100:1, BTW.) Sowter certainly is well regarded, although I did not associate them with making audio step-up transformers to drive ESLs. Sure, go for it. My recommendation of Plitron was solely based on the idea of your driving the speaker with two transformers (one for bass and the other full range) and dumping the RC network in the process. However since you are venturing into the unknown, you might want to find a way to experiment with using a single 1:100 step-up before investing in a custom build of two of them. (Acoustats are not identical to SLs in terms of stator to diaphragm spacing and bias voltage, although using separate bass and treble transformers was originally the idea of Acoustat, borrowed by SL in the late 90s or so.)