I don't think there's any point in returning him to his breeder at this stage. A week ago, perhaps, but not now. If you can find him some puppies close to his own age to play with regularly though, that would be extremely helpful to him. When he reaches 10 weeks old, enrolling in a puppy kindergarten class (which is primarily about socialisation, btw, not really about training) would be a very god idea. And if you don't happen to already know anyone with a suitable pup for him to play with, you might be able to find some willing playmates at class (for playdates out of class). So the socialisation possibilities are out there if you look
As for bite inhibition, yes, you'll probably find it harder than you would have if you'd brought him home at 8 weeks. That doesn't mean that an 8 week old has fully learnt that lesson - far from it. When we rehome pups at 8 weeks, we're interrupting their education. But they did at least get part of the lesson learnt from their mothers and littermates, and their new owners have only to continue/build upon that. You've got to start from zero, I'm afraid.
Here are a few recent threads about puppy biting and teaching bite inhibition (note that that is teaching the pup to use his mouth gently, not discouraging him from using it at all
) that should help you out a bit:
Puppy Biting HELP!!!
In addition to time around other pups, here are a few socialisation ideas that you might find helpful: www.boxerworld.com/puppy/socialisation