Hi, guy, I suspect the problem is that an octave above middle C really is quite high for most tenors. Counter tenors can sing that, or higher, but they are an exceedingly rare voice type. The samples you bought may be giving you a more realistic idea of what you would get from a group of vocalists than your composition software. It's not that men who can sing that high don't exist. That is technically a range some tenors can sing in, but only a tiny number. Take a look at some standard choral repertoire and you can start to get an idea of the more commonly used parts of the range for different voice types. And remember that it is only in modern times that we have started using the "modern" tuning. Historic pieces look like they are written higher than they actually were, because the composers and singers were using a different tuning standard when they were written, and they are still performed down at that historically accurate tuning today.