Frankfurt wouldn't be able to win Napoli home and away,the club don't have the experience and players to win Napoli. As we all saw in Napoli's last match,they dominated and qualified easily to the next round. Napoli has a better chance of winning the match and will definitely qualify to the next stage. It is in the next stage that they might find it difficult to win the club that will be playing them. Don't get me wrong, I am not underestimating Frankfurt, they might shock me but this is my own observation from both clubs.
No one doubts Napoli this season in the Champions League as long as the opposing team is not a top team. Frankfurt is a team that has no better chance of qualifying for the quarter-finals, so it is true that Frankfurt will be very likely to fail and end their adventure this season at the Diego Armando Maradona Stadium.
I'd be really surprised if Napoli didn't qualify, that would be unbelievable. But I don't think that's going to happen, it's nearly impossible when they're in such really consistent form this season. For Serie A teams, I think only Napoli are the most convincing to qualify for the final this season, while Milan and Inter are not in my consideration.