Depends what exactly you are looking for when you want Rich Timbre.
To some richness evokes a fullness of tone, where you really feel for instance the weight and presence of a tenor sax in the bottom registers or whatever, that may be thinned out in other speakers.
It that is what you mean by timbral richness, I'd throw the Devore Fidelity 0/96 and /93 have in that camp. That's their specialty. Big, Rich, Thick full sound, so you feel that a piano or acoustic guitar has a vibrating sounding board, low strings vibrate the air, voices have a "chest" projection and not just disembodied mouths.
On the other hand my you mean something more like Timbral accuracy, in the sense of bringing out the specific timbral characteristic or tonal color of voices and instruments - e.g. that a brass cymbal really sounds like brass, a struck triangle silvery, a trumpet warm resonating metal, the special combination of reedy/breathy/bell of a saxophone, wood sounds like wood, etc.
I've always looked for "Technicolor Sound" in the sense of a speaker producing a wider array of timbral colors, because through most speakers I immediately hear a homogenization, an imprint put over everything by the speaker. Once I hear a sax, or trumpet, or cymbals on a speaker it's not long before I pretty much know what those will tend to sound like forever more on that speaker - unlike the truly endless element of "surprise" found in real life in that regard.
In that case, among the best I've ever encountered are the Joseph Audio speakers. They are very accurate but with a particularly grain/haze-free sound. Just the way colorful pebbles are more richly revealed through a clean, clear stream than through one full of fine silt, I find the timbral colors of voices and instruments seem more finely and purely revealed from the JA speakers - a greater "rainbow" of timbres and tonal colors seem to get through. At least that's what I hear, though that seems to be echoed by a great many other people who hear them as well.