It sounds to me like you have not shown him, or had his health testing. I am not sure what ACA is, but I would never purchase anything that was not AKC. Do you know anything about the dogs behind him? How about their health testing? Were his parents hips and eyes tested? Boxers have alot of health problems, I would personally just neuter him, becuase it doesn't sound like you are ready to breed. What if he gets an doggie std, or other problem?
because you think your dog is great is not a reason to "stub" him out. Has he had his testing done? Is he within the standards? Does he have a championship in the show ring? Does he have Herpes? How many dogs are in your local shelter? Well probabay about 50% of them are there because people just had a cute loving dog that they wanted to "stub" out and more than the 50% will die because they cant find homes alot of which is due to backyard breeders "stubbing" out their cute dog.