Karla, I think that it is very possible for our names to be a shortened or even lengthened to be more appealing to pronounce. So far, my Seither line has gone back to a Jakob Seither in Rohrbach Germany and he would have been born in about 1775. This info has come from another Seither in a town near Rohrbach, however, he said he hasn't found the link between the Seither's in the two towns.
I would like to know more about your line. My Grandfather Freidrich Seither left for America at the age of 20 from the seaport LeHarve, France and settled in Philadelphia.
In a letter that he wrote of his life he stated "In the northwest (in ref. to Rohrbach) toward the south is the Bohemian Forest" So I guess that the Seithammer's and Seither's weren't to distant from each other!
Sorry I don't have anything of great importance for you, but hope you will write back soon.