In Schubert’s “Am Meer” from his song cycle Schwanengesang, he introduces and concludes the piece the same way. He decides to be a little unconventional and has a Ger6 chord resolve to a I chord in C major. He uses a D# for the me instead of a Eb, but enharmonically they are the same note.
The recording I found on Naxos of Benjamin Luxon singing “Am Meer” is absolutely gorgeous. The piano part plays with the voice with its sweet opening into the intense middle section of this piece. The form is ABAB, where the A section is slower and more serene, and the B section is darker and more intense. The transition from A to B is exactly the same each time, and the introduction and the conclusion are the same as well. The words change in each verse but the two A sections are rhythmically identical, and the same goes for the B sections.
Since the augmented sixth is a part of the accompaniment in the introduction and conclusion I would just put a lot of emphasis on it. Since it is followed by a major I chord, I think it would be best to accentuate the oddness of it and bring it out a little more over the other parts. I really like this piece because it is so insecure, where the listener thinks it is a smooth ballad then suddenly it is not. It almost seems like its predictable, but when listening to it, the transitions are what give it away not the vocal line itself. I like that the augmented sixth does not resolve like it should, because again it is a small trick played on the listener. Schubert was very crafty with this piece of music.