I can kind of see where you husband is coming from with Rex - but think it's only a problem when combined with Felix. Either are fine alone. I once taught a class which had Rex, Felix and 2 Kittys - there was a standing joke about us being the Petshop Class.
It seems like the alternative/slightly American sounding market has been well and truly cornered in your family!
So how about going more 'mainstream but underused':
Adam, Anthony, Adrian, Alistair, Christian, David, Edmund, Gareth, Gregory, Ian, John, Joel, Kenneth, Michael, Martin, Paul, Richard, Robert, Simon, Stephen, Timothy
Or more alternative on a nature type theme:
Rowan, Robin, Jay, Birch, Blue, Skyler, Bear, Orion, River, Storm, Red