I keep coming up empty handed with obtaining information on my great great grandfather Johann Karl

From family notes Johann was born in Nassau, Deggendorf, Bayern, Germany. He married a woman with the first name Maria.

Johann had at least one son, Michael John Karl, who came to America in 1881, Became a naturalized U.S. citizen in Oct.1886.He Traveled back to Germany where he married Agnes Staab (b 1/20/1860). They returned to the U.S. in 1892.

Based on the above information, could some help me track down the names of my great grandfather Michael John Karl's parents and the name of any siblings?

Thanks!