Is this a problem with sperm quality or egg quality? If you've had miscarriages, it's most likely a problem with your eggs or your ability to carry to term. If you want to try different sperm, however, I think you should start doing something about it soon as your prospects get smaller after age 35.
If you've identified sperm as the problem and you want to try different sperm, there's no choice but to bring up the subject with your partner. He can only tell you how he feels about it.