The line in can take a hot signal according to guysonic. Most likely you won't ever need an attenuator for a board feed, but hopefully members with experience using the HR for board feeds will chime in.
I've had a distorted recording from a hot SBD patch once, where it was so hot that I had to keep the level on the R-09HR really low, like about 3-4 or so, and there wasn't time to ask for a less hot signal due to the show starting. That's one of the reasons I switched to a Marantz 661 as it can handle a much hotter signal with its pro line in.