I’m loving the name more and more everyday. [name]One[/name] problem though, I’ve been saying the full name out loud to myself ([name]Miles[/name] [name]Haynes[/name]) and I can’t tell if it works. Too many "s"s? Immediately I think of [name]Miles[/name] [name]Davis[/name], which I think sounds quite nice. Any opinions appreciated.
I see your concern. [name]Miles[/name] and [name]Haynes[/name] are both single-syllable names that end in an S, whereas the surname [name]Davis[/name] has an extra syllable to offset the S’s. However, I personally don’t think [name]Miles[/name] [name]Haynes[/name] is that bad, especially if that’s the name you love. I used to love [name]Miles[/name], but I soon fell in love with the name [name]Walker[/name], then the name [name]Lane[/name], and I couldn’t do that to a family: [name]Miles[/name], [name]Walker[/name], and [name]Lane[/name] sounds like we just love going for a stroll. 
(Thankfully my husband only likes [name]Lane[/name].) You may like either of those suggestions, though: [name]Walker[/name] [name]Haynes[/name] (awesome!) or…wait, [name]Lane[/name] [name]Haynes[/name] won’t work. 
The short answer to your question is, in my opinion, [name]Miles[/name] [name]Haynes[/name] may not be a perfect flow, but the more I say it the more I like it anyway.
I don’t particularly like the sound of [name]Miles[/name] and [name]Haynes[/name] together. Why not [name]Milo[/name]?
my DH’s name is [name]Myles[/name] [name]Leon[/name] [name]Rey[/name]. It works for him, but it can seem very staccato when spoken. I think that [name]Miles[/name] [name]Haynes[/name] would be similar, but I love the sound of it and it would be a great choice. (i’m a little biased though)
When I say [name]Miles[/name] it’s more like two syllables, and I think for most people it’s 1.5. I think matching z endings are more stylish than some.