With satins, you have to breed with rabbits which have demonstrated an ability to develop into adult weight, both buck and doe. It's as simple as that.
When Maryse had her litter in April, she was barely over 6 months of age and over the course of raising that litter (and she was an excellent mom, might I add), she became thin as a rail. I mean she really looked frail when I weaned her litter off her in the early summer. I fed her rolled oats to try and spark her apetite to the point that she would eat and put the weight back on, and it's worked very well. In fact, it's worked so well that I am about to take her back to the showroom after a 6 month hiatus at the end of this month. She looks better today than she did in late February when she was shown in Anderson, MO, and she was 1.5 lbs. underweight.
How well it will work will be limited, however. Once again, part of the problem is genetic while often times, part of the problem lies with their diet. An 8-month old rabbit should be somewhere around 8 pounds as a minimum, while 9 pounds is more desirable. I registered 3 rabbits earlier this spring which tipped the scales at 10 pounds each.
Breeding with good rabbits which display good weight gains is critical, but it can also be tricky because with this breed, they so often will develop later than even their litter mates.
The best thing I can suggest to you would be to keep an eye on a smaller rabbit which has big feet and good type (rise from head to loin, stocky shoulders, etc.) but maybe hasn't put on weight like you would've preferred. In my experience, they are usually the ones which will make weight for you later on.
Others to keep your eyes on are the young rabbits (3 months) which maybe are slow to develop, but have rock solid flesh. I have a white buck named Y2J. He was the 5th rabbit born in the Maryse litter I crow so much about on here. I didn't take any profile pics and post them a couple of months back, mainly because at the time, I really didn't think too much of him. I will guarantee you that most other people wouldn't have either, and he would have wound up in a meat pen. At his first show, he was the first rabbit off the table in an 8-rabbit class, but right now, I really wish I had taken those pics so that I could have shown what a difference a little time and patience will sometimes yield. The one thing about him which told me to give him a chance was that his flesh was bowling ball solid. Sure enough, he has continued to develop and now is a pretty sharp rabbit AND one of the best-sized in the litter, as well.
