Personally I have always found the mouthpiece has more effect on the sound than the instrument. Of course the largest factor is yourself and your mental sound concept, but after that the mouthpiece has a bigger impact on the sound and the actually instrument itself less so. The instrument simply needs to feel comfortable to hold and play and have a feeling of notes slotting in place where you expect them to. If your sound concept is on the darker side then try a mouthpiece that helps match that sound. A few suggestions would be Curry TC cup (in whatever diameter you play) or if you can find one, the Bach straight numbered mouthpieces, ie. “Bach 3” (not 3C just 3) That’s what Chris Botti plays on (and yes, he also plays a Martin Committee)

The Bobby Shew horn is extremely versatile and very mouthpiece sensitive meaning it can be dark or bright depending on the mouthpiece and the player’s approach and sound concept.

Hope that’s helps.

Simple answer, plays what feels good and gives you the sound in your head, you might need to try a bunch of different horns/mouthpieces to find it.
-Alistair