As everyone has said above, 83% apparent attenuation is pretty darn good. Trying to squeak out those last 6 gravity points is probably not worth it. The enemy of good is better. I don't recommend it, but some people will try champagne yeast. I am not a fan of it. The other option is a lager yeast because they metabolize/digest raffinos which ale yeasts can not. IF you choose to go this route, you need to work up a starter to high krausen and then oxygenate the starter a few hours before you pitch it into your beer. I would be surprised if the hydrometer moves even with this. Something tells me you have fermented out all of the fermentables. As Mark said above, Brett will DEFINITELY get your FG down, but will change the beer. I love Brett character and am comfortable with using it and sanitizing everything, but you may not? I would be happy I have a beer with 83% attenuation that tastes great! DO NOT USE BEANO UNDER ANY CIRCUMSTANCE ,NO MATTER WHAT ANYONE TELLS YOU!
Next time if you are shooting for 1.008, mash a couple of degrees cooler. Add your sugar at high krausen. Yeast are lazy an will metabolize the easiest food source, i.e. simple sugar. Adding the sugar later will likely get you your magical FG. Pitch an appropriate starter cool and let it free rise, then as it ferment starts to stall (usually around day 5, but watch it to be sure) get it to a warmer ambient or ramp up the temp with a belt or heating pad, or etc. You could also try a different yeast, but I would try the other stuff first if you are happy with the yeast ester profile.