Your speculation about the transformer-coupling being the differnce is interesting. You don't mention your interconnects, but I wonder if there could be some sort of subtle noise or ground problem present in your system normally, which is alleviated with the tranny inserted in the loop. Is it at the inputs, outputs, or both? As a side note, I believe I remember seeing a new brand of 'preamp' being advertised on A'gon a few months back, which was, if I am recalling correctly, basically just an input selector with transformer coupling and attenuation, but I can't think of the name (it had a fancy wooden case, though). Have you ever tried Rowland in your system (also transformer-coupled)?