You pretty much have it. At Audi it goes like this...
S-line = trim package with nearly S-spec interior, S-car looks but normal engines
S-car = high performance, S-spec bumpers, S-spec interiors
RS-car = highest performance, RS-spec interior (Recaros optional, better leathers, wider weave carbon fiber, etc.), RS-spec bumpers, RS-spec flared fenders, etc.