Jolida Foz SS-X Tube buffer & soundstage expander?

Hi there, I recently purchased this item, to try it as a replacement for my WLM EQ (between music server and integrated tube amp). It does everything as advertised and mentioned in this thread. I struggle with one drawback, however, and that is slightly more  emphasis on sibilance (I can't stand that). There is no change in the high quality interconnects and power cable connected to the unit (same as to WLM) so the problem is in the new unit. I am trying tube rolling without major improvement. Any advice?