General rule for suspensions
Set the pre-load first (rider sag)
Check static sag
Set the rebound (if adjustable)
Set the compression (if adjustable...some even have both low-speed and high-speed settings)
Pre-load should be set such that the bike is sitting (at rest) at the 1/3 travel point from full extension (rear wheel off the ground) with the bike normally loaded (you included).
The K1200RS/GT rear travel is 6 inches (well, really 5.9+), so the pre-load setting should be 2 inches. I don't know what the suspension travel of the K-S or K-R is, but the pre-load should be set at about 1/3 of the full suspension travel.
Static sag...I can't remember the numbers, but it's more for getting the right spring than an adjustment. It has to do with how much the spring compresses in millimeters between a totaly unloaded to the bike (again, rear wheel up in the air) after the pre-load is set, and when the bike is at rest, unweighted by anything on the bike (no rider, no bags, etc). If the distance between the coils is small, the spring has basically been used up just by the pre-load, and indicates that a heavier spring is needed. If there's a larger distance (and again, I need to find the numbers), then you might need a lighter spring. However, after saying all that, most bikes come with a spring for a 160-180 lb/75-80k rider. If you normally have an additional 100lbs./45k weight on the bike, you should consider a different spring, and then you have the opportunity to have someone set the shock up per your specifications. Same if you are around 100lbs. dripping wet, but you also need to share your secret...
Rebound: When the shock returns from a compressed situation, adjust the rebound by decreasing the damping until it overshoots and returns to the normal rest point, then add damping until it stops at the normal rest point without overshooting. The object is to get the shock back to the normal rest point the quickest. Too little damping and it overshoots, taking longer to get to the normal rest point. Too much, and it's too slow getting to that rest point. A very slight overshoot would be ok, one that's barely noticible.
Compression is more of a user-feel adjustment. You don't want the suspension to bottom out (too little damping), but you don't want the bumps and jolts (too much damping) transmitted to the bike (and to you) if you can avoid it. Low-speed compression (0-2 inches/second) is for bumps and pavement irregularities, and the high-speed side (2 inches to 15 feet/second) is for potholes and badly maintained railroad grade crossings. Low-speed is something you can play with over time riding various roads. Good place to start is the mid-range setting, and based on the feel, adjust as you like. Don't go more than two clicks at a time, though. If you end up with the adjustment at one end or the other, it could be time to have the shock rebuilt and set-up for you by a suspension shop The high-speed circuit should be adjusted fairly close to the same setting as the low-speed one, then on or two clicks one way or the other depending on your "large-bump" experiences. Hopefully, you don't have those.
On the stock rear shock, you should have a triangular-shaped knob (although some have reported that it's been broken off, in which case you have a round black plug) at the bottom of the shock body. If you have one, that's the rebound adjustment. Counterclockwise to make the suspension perform like a pogo-stick, clockwise to slow the rebound speed down. White spring, right?
The original post was for shocks in general. And, in general, if you don't have any adjustable shock options, you want to keep the shocks you have AND they're rebuildable, you can take them to a suspension shop to have them rebuilt. Tell them what you don't like about the existing shocks and they should be able to rebuild them for a better ride. Based on one shops owner, the stock BMW motorcycle shocks aren't easily (meaning time consuming and therefore more expensive) rebuildable.