I just want to tell you I think it's amazing that you feel this way, and I truly admire your selflessness in wanting to donate any extra embryos.
I find myself in the opposite camp. We didn't have any embryos from our first IVF, so it wasn't an issue, but do have 4 frosties left over from IVF #2. This will be our second and last child, that we are sure of. Both DH and I, while we wish we could be as generous as you, simply feel like we would be donating our child, that it would be an adoption of sorts, and we just aren't comfortable with the thought of someone else raising "our child."
We are waiting until after LO's birth to make any final decisions, as we have one year of storage included with our IVF package, but will likely donate them to science as what we consider a compromise: hopefully helping others in that way, if not with the direct donation to a couple.
I don't really have any answers, but did want to share my story. I can't imagine how difficult this difference of opinion between you and YH husband must be, and I truly sympathize. Again, I commend you on your stance, and wish you all the best as you two come to a decision in the future.