I actually forgot about the beer, so it wasn't the reason I find Conrad more serious sounding than Killian. I think it might be Killian's bouncing syllables; that "illi" in the middle is very high energy to me, so the whole name sounds jovial.
I like your reasoning behind Trey, even though I don't like the name itself. I'm sure your son will like the connection to both you and his brother. :)