Rear Brain Shock:
Riding Weight + 10 is a good starting place for the rear shock. When checking sag, Spec recommends that the Brain Fade (blue) knob be set one full revolution back from full firm (full firm= full clockwise) and the Rebound (red, on actual shock) at three revolutions back from full slow (full slow rebound= full clockwise). Push the o-ring up to the seal on the shock. Sit on the bike for a minute in your riding gear. Get off and check sag. Should be 8-12mm to the O-ring. Once you dial in the pressure, then re-set your Brain Fade and Rebound to your liking. I typically ride the BFade about 2-3 clicks back from full firm for lots of climbing and getting to/ from trails, and open it up between 3-6 for descending, but I come from a HT world. You can go further for a more plush ride. I ride my rebound about 1/3-1/2 back from full fast, and make adjustments on the trail. If I feel like the bike is bucking me forward out of little rollers and boosts, then it's too fast.
Rock Shox Reba:
The air chart for your positive and negative chambers should be on the side of your fork lowers. For the weight range of 180-200 they suggest a starting point of 120-135 in both chambers (so, for 190 riding weight, maybe 125-130? 127.5?
). There seems to be some growing consensus that the fork performs really well with 10-15psi LESS in the negative chamber than in the positive. What I've seen suggested often is to let all of the air out of the negative chamber, then fill up your positive to the recommended setting and check sag [make sure your compression damping is open (open= counter-clockwise). Sag should be 10-15% of travel, which is 100mm, so you want between 10-15mm of sag. Then, begin to fill the negative chamber and watch the stanchion at the seal. As soon as the fork starts to get sucked down into the lowers, stop adding air (or even let a tiny bit out). Seems most people are finding that spot to be about 10-15psi less than the positive chamber.
Rebound is similar to the rear- I ride mine about 2/3 of the way towards full fast, but there's a lot of personal preference in this. Too slow, and the fork will pack down (it won't rebound back to full extension between bumps, therefore, "packing down") over multiple, fast bumps. Too fast, and it'll kick you up off of bumps and might be twitchy/ chattery-feeling in tight, fast turns.
Compression and Floodgate: Still a little bit of a mystery to some and lots of differing opinions- search the forums. Basically, I ride mine with compression locked out (clockwise) and floodgate 1/2-2/3 closed/ firm (closed=fully clockwise) for most climbing/ flat, rolling conditions, and open up the compression (without touching the floodgate) for descending. Sometimes, I'll leave the compression closed and open the floodgate back a little if I feel like I'm getting too much brake dive/ compression in tight switchbacks on the way down. Still experimenting with this and, again, lots of personal preference for riding style.
Just my two cents- I'm sure there are others who will disagree with some of these suggestions- and I'm always open to learning more about this fork.