I guess it'll be a fennec?
First of all, the ears are going to be visually enlarged by the fur being added on. Make them smaller. They will be massive windbreakers and I've had issues with wind when wearing my toon suit, which has ears maybe 1/3rd the size of yours.
I'm not an expert with foam based heads, but as far as I know now you shape the head. Smooth the edges a bit so it is a nice form.
Any further steps are beyond my knowledge though ^^"