I think Fergus could work. But I think Felix would be way over the top with your last name with the x's at the ends. Although an x is actually a ks sound with s at the end of it. Would you like Freeman or Furman or something like that? I also love the name Dashiel, and would think it has three syllables. If you want it to be two syllables just spell it Dashel or something like that. I think that comes down to people just speaking quickly. For instance, I consider Maverick as being three syllables, but people say things so quickly, it comes out with two syllables, then they think it is two syllables after a while. There are a lot of names and words like that. Anyway, good luck!
