What does your team look like? It completely depends on the team: who would Soriano be replacing? Who would you be replacing Broxton with (and who is your other closer)?
On it's head I think it's a pretty fair deal, value-wise, so I can't say you're 'winning' or 'losing' this deal, it just seems like a fair deal. But as I said, it depends on the other elements of your team.
Alright, so here's what I think: You're replacing Bruce (big-time power, decent speed, terrible BA) with Soriano (good power, good speed, terrible BA). And you're replacing Broxton (tons of saves, great ERA and WHIP, almost 2 K's an inning) with Lidge or Gregg (both decent closers, though Lidge has been a disaster this year).
No way I'd do this deal. Do you need the extra 5-7 steals that bad? Because that's all you're getting out of this transaction, and you're losing the extra power numbers that Bruce provides. Meanwhile you're downgrading pretty substantially at RP, going from the best closer in the business to an average or below average option. Not a chance in hell I'd do this.
Broxton is a beast. But Soriano has a history of doing very well in the second half of the season. For me it would be a no brainer to land Soriano. He will hit a ton of home runs in the second half. My guess is he will hit over 40 home runs. You won't get that from too many ball players. I would trade Broxton for Soriano.
I agree to see if you can land a better OF for Broxton, but if not, I'd probably still make the deal, get Soriano and is there a way that you could get both Lidge and Gregg? If so, do that. The two of them combined should get you what you'd lose by giving up Broxton, although you'll take a hit in ERA and WHIP.