I shoot an earlier Knight Model (USAK that still uses #11 caps for ignition), but I think a lot of things are similiar for Knights.
Like SamStafford said, I highly recommend loose powder over pellets. Loose is more controlable and more adjustable. I've settled on Triple Se7en powder for now as the other substitutes like American Pioneer, BlackMag, Shockey's Gold are less powerful and have issues with moisture. If you have access to true 2fg black powder like Goex, Elephant, etc I would definitely give those a try too.
Fight the urge to shoot lightweight bullets at hyper velocities - that works for centerfire rifles, but not so good with muzzleloaders.
I've found that sabot bullets from 300gr up to 400gr give me my best accuracy and have been devastating on game.
As arcticap suggested, the MMP sabots have always worked marvelously for me.
As far as bullet choice goes, the Hornady 300gr XTP Mags and 300gr SSTs give me fantastic accuracy over 80gr of 2fg 777 powder. The bullets made by
http://www.prbullet.com/ have worked well for me and are my hunting bullets of choice.
Since you'll be using 209 primers in the Disc, I would suggest doing a little research and see what people say are the "coolest" brand of primers - as 777 powder can cause crud build up around the breech plug with really hot primers and loads..............plus really hot primers can actually start moving the bullet before the powder fully ignites which can hurt accuracy.
That should give you some food for thought for the present.
Good Luck