I recently went back (Waaaaay back) and listened to episode 3 of WoodTalk when the subject of soundproofing and noise control came up. While there were some good suggestions on the show (and in some other threads here), most of them are geared towards trying to keep the noise confined within the shop.
Another step that might prove helpful is to try to dampen those pesky dBs at their source (i.e. the machines producing them). There's products from the automotive industry that very effective in reducing ambient road noise from tires, exhaust, engine, wind, etc. One such product is Dynamat which comes in a peal and stick application. You could line the machine cabinets with dynamat to reduce noise generated from the motors and vibration they generate.
I haven't tested this, but I'm willing to bet it would make a noticeable difference.