You come across a door, guarded by two mysterious men.  As you start to figure out how to tell which one is lying and which one is telling the truth, they say in unison:

> ***WELCOME, TRAVELER, TO REIBELLO'S RIDDLE REPOSITORY.  SHOULD YOU SEEK ENTRY, YOU'LL HAVE TO SOLVE A SIMPLE PUZZLE.***

You quickly agree to hear the puzzle.  You also notice that their voices are different.  One is deep and **strong**, while the other is softer, and strangely *emphatic* about his words.  

>**Our first AND second facilitate, that which you need to operate.**

>*Each alone, is not correct, but read aloud make our subject.*

>**Our third is imprecise at best, but gladly taken on a test.**

>*Our fourth is five-* **IT IS TWO!** *We disagree.  But it's also half of twenty-three.*

>**Our fifth is fifth.  All the clue you'll need, I reckon.** *But just in case, it's also our second.*

>*Our sixth and last, core of our planet round, but don't go quite as far in underground.*

>***Our riddle complete, answer if you dare.  Six letters, and no more, WE SWEAR.***

What word are the mysterious men looking for?

I have an alternate line for letter 4 - tell me if you think it's better / worse / easier / harder please and thank you.
>*Our fourth is five-* **It's two.  His clues are the worst.  It's also half of what is first.**