Four of the five have responded so far, with useful and hardhitting feedback. And since three of those four objected to the same opening narrative tack, the first order of rewriting business came home: get it going more quickly and clearly by finding some way to portray a character who's already been killed off-stage. His death off stage isn't the problem--the resulting backstory is. Somewhere there's a lightning way to plant this character in readers' minds...without compromising the first person p.o.v...a way that leaves readers thinking 'Bummer, I'm really sorry he's dead."
One of the four objected to the killer clever opening, pointing out a line further on down the page that he felt was the right spot to start. He was right. The killer lead was cute and controversial, designed to get attention fast. But it required too much explaining: I didn't really mean that in the sense I know you thought, etc. A man brooding on his client's murder would certainly be in a much grimmer mood, best expressed in the suggested line.
Two big lessons sprang from the feedback. First, be grateful for hardhitting feedback, expressed and in between the lines. Betas in this instance had only a handful of pages and no outline to sketch out the story. But enough expressions of 'This may be cleared up later' are a strong indication that things need to be clarified more quickly now. Second, if the betas echo a little voice inside you you've been trying to ignore, then admit that you've known what to do all along: I too had wondered, several times, about starting the tale at the line recommended by that one beta.
Oh, and make that three lessons, for here is the third: We owe our beta readers. Let their markers be well placed.