modifying a w4s dac 1

I am considering changing the output stage on my w4s dac 1. I want to see what it would sound like with an op amp free output stage. Has anyone modified one? I was considering either a simple transformer coupled arrangement, or may be even a long tailed pair valve stage. This is all based on the assumption that what is good for the twisted pear ess9018 architecture will read across to this one. Ideas please and does anyone have a schematic of this dac.