It's really encouraging to have a developer asking the audio community how to better communicate with us! You ask a very good question. For me here's what seems to work best:
- A list of 3-5 adjectives of what you want the player to feel while playing the game and hearing my music.
- A list of 3-5 references that you feel would match the game's needs.
This way I have a broader spectrum of what you're after instead of just one piece and that can help avoid the "it must sound like X" problem you mention.
Edit: It's never offensive to me to hear "I love composer X and want the music to be like that." as long as my client understands I'm not that composer and will bring some of my own indentity to the music while aiming to hit the goal(s) as closely as possible.