You'll hear some fine duets and trios in Mozart. My favorite is Bei Männern, welche Liebe fühlen (lyric baritone & soprano) from Zauberflöte/ Magic Flute. (Don't worry if you don't recognize the words - it's all in Swedish. Bergman. Best movie of Magic Flute ever made. I believe it's still available.)
There's a nifty duet in the same opera by the two armored men guarding the dungeon . . . Der, welcher wandert diese Straße. Hang with it and you'll hear the tenor/soprano duet afterwards. Plus you can hear real soprano fireworks from the Queen of the Night. This is an excellent version (I have it): Von Karajan and the Vienna Philharmonic
About the only place you'll hear a Heldentenor is in Wagner, and "fresh" is not the first thing that comes to mind when I think of old Richard. Mozart is the place to start - he has a much lighter touch.
Thanks for your (invaluable) 2-cents, AAM! I already love Mozart but haven’t paid any heed to his opera.