This would narrow down to only the people who have tried M-80s and feel they can compare to some IEMs. Or people that can find similar frequency response graphs, but the graphs cant exactly tell you what they sound like.
But I guess thats the point of posting this on this site.
The Denon C300 are closer to M80 with powerfull bass, crisp clear mids, highs and wider soundstage with good imaging and instruments separation. Sony EX1000 are also amazing sounding IEMs with less bass punch than M80 but if you add ZO2 then it willbe there.