Note: here I use gxargs and ggrep instead of xargs and grep commands because my OS does not come with GNU xargs and GNU grep by default.
$ find . -type f -not -name '*.aiff' -not -name '*.8svx' -print0 | \
gxargs -r0 ggrep -bZl '^FORM' | \
gxargs -0n1 xxd -p -s32 -l2 | \
sort | uniq -c