Why don't you email Jack at Woo Audio. He is extremely helpful. He would know best.
Can you take a close-up of the output transformers, or are they mainly hidden inside their covers? I have searched a number of Woo 5 threads and the Woo web site and links and there just isn't much reference to the output transformers, their specs, construction and materials. My experience with SETs is that the output transformers can have a very significant impact on sound quality, but that good ones are very expensive.