Sound was fine for Soundgarden, but yes I agree it was too quiet for everyone else on the main stage before them. My guess would be they didn't want to drown out the shitty little stages that were close by, but after about half an hour of Soungarden's set there was no one else playing.
I watched the first four songs of Skindred's set, but their sound was so poor I couldn't be bothered with the rest and went in search of food. Skindred annoy me though. Massively heavy and bags of groove live, basically an indie band on record.