This is from Jayson Stark's latest trade deadline update:
If there's a hitter who might have even a remote shot of getting traded, the Pirates have asked about him. One surprising name they took a run at: Kansas City's favorite All-Star folk hero, Billy Butler. But the Pirates are still in a buy-low frame of mind. And the Royals have told a few clubs that inquired that they'd have to be blown away to deal their All-Star.
He also connects the Pirates to Hunter Pence (though I read that as speculation on his part). Bill Center at the San Diego Union-Tribune lists the Pirates as one of "seven-to-ten teams" in on Chase Headley.
There's plenty of speculating that can be done here, but really, it seems to me that the bottom line is that the Pirates are interested in adding a bat to their lineup, that they don't necessarily need to just get a rental player if the right player is available, and that they have a ton of flexibility as to where said additional bat could play (four corners, shortstop). They're also not likely to overpay for said bat, which is why they're not leaving any stone unturned at this point. What's actually going to happen? From here, your guess is as good as mine.