It doesn't matter as much as you might think. In this case the nickel and chrome finishes are plated onto solid brass base metal, then polished or brushed and a thin coat of lacquer is applied. The first plating for both finishes is nickel, then the chrome is plated over top of the nickel giving it a whiter/brighter hue. Nickel finishes are slightly darker in color giving them a warmer appearance. Satin nickel matches satin stainless so closely you usually can't tell the difference even when they are side by side. Since most stainless steel architectural hardware is made from type 304 stainless that is composed of steel, chromium and nickel, they are all very close in color and appearance. Stainless steel isn't as soft and malleable as brass so hardware made from stainless steel is typically more modern or contemporary whereas brass hardware will have more detail. Ultimately satin nickel and satin stainless finishes match well so you shouldn't be concerned at all when mixing the two.