Initially, as in all things, the quality of components is key. One cannot go too far wrong when you start with quality materials. I, like most, am too poor to buy cheap.
Fundamentally, one must not lose sight of the final product – no one element should overpower the ultimate desired result. For chocolate, anything added to chocolate should be present to complement the chocolate, not overwhelm! While presently hot spices are trendy, such flavouring should enhance the chocolate, not be the primary taste. While spicy components, such as cayenne pepper, is more dramatic, some flavour tones are more subtle – primarily estate and origin chocolate. The differences in taste come from the variety of cocoa, the terroire (climate, environment, and soil), and the processing. Some differences are more apparent, but others are more subtle. Chocolate has over 800 identified flavour components, while red wine has a paltry 500.
What is unique or unexpected now, has been in use for at least centuries or, indeed, millennia. Spicy pepper has been in use with chocolate for over 2,000 years. Other flavour elements have been used for centuries – ginger, garlic, onions, and so on. The only difference is the current trend or acceptance. One cannot overlook any combination that does not destroy the ultimate desired result. I made a gelato, for fun, for a blind tasting – it was a spicy salami gelato. It was considered quite controversial, but ironically, nduja is a very traditional gelato flavour. Very little is new in the culinary and design world.
In conclusion, the ultimate combination for a quality finished product is quality of initial product, knowledge of ingredients or elements, and good taste.