I have a couple recordings in my "demo tracks" that I find are good at revealing system effects on sibilance--Rutter Requiem (Reference Recordings--Redbook, but an excellent recording) and The Addicts' Rehabilitation Choir (Mapleshade--again great Redbook recording). Both recordings are choral music, and if there are issues with cables or electronics the "ess" sounds will not sound natural, but if everything is ok, they sound as you'd think they should.
I've found cables to have a pretty big effect on sibilance, followed by DAC. My line stage (first Rowland Consummate, then PSE hybrid, then Parasound JC2) didn't seem to have a big effect on sibilance, although I heard major differences on transparency and clarity.