I can empathize with you.
I can not speak for your husband, but my husband and I have come up with our own method of deciding how many children we will eventually have. In actuality there is not a set number at all.
Maybe these will apply to you as well:
Aside from my (and your) desire to have many children to love, first and foremost, it depends on how many children God will bless us (and you) with. Second, it depends on how well my body (and your body) will handle the pregnancies. Like others have said, obviously finances have to come in to play as well, but I do not think that should be a deciding factor. My love is never ending with my children. If it came to it, I would rather have a smaller house with more children, than a empty mansion.
My husband and I have a 3 year old, 1 year old and are currently expecting. Although I am currently expecting, I am already planning when we will be having baby 4 and 5. But to stick with our method, we are taking it one at a time: If 3 seems like to much, we will stop at 3. If not, we will have another, and if 4 is too much we will stop there, etc, etc. Who knows, maybe we will be blessed with 10, maybe 4. When people ask, "Is this the last one yet?" I get so frustrated. Not only do I truely not know the answer, but many people can't phathem the thought of having more than two children. Everyone has their own ideal of a perfect family.
As far as right now, I can not see myself ever not wanting more children, but the factors (like mentioned above) have to be considered. For example, if my pregnancies became more high risk with each one, there would be a point where I would have to stop.
If you are really set on having more, then God bless you. If you already have 8, I do not see why having one more would be of too much concern to your husband. Maybe he just fears that it won't end there either. There does have to be a common ground, and I hope you can reach it. Was he okay with every previous pregnancy? If yes, and now he thinks having another would be too much, than you probably have a good chance of convincing him otherwise. If he said no more, two babies ago, than maybe you should just sit back and be patient with him.
Either way, let us know the outcome!