How to replace with "sed" some hex values by other hex values?

Assume I have a file \usr\home\\somedir\myfile123.txt
and I want to replace all occurencies of the two (concatenated) hex values x'AD' x'A0' bytwo other (concatenated) hex values x'20' x'6E'

How can I achieve this with the gnu sed tool?
Additional question: Is there a way to let sed show the number of replaced occurencies BEFORE or AFTER the run?

Hi,
Examples ( '$' is my prompt ):

$ echo -e '\xad\xa0' 

$ echo -e '\xad\xa0' | od -t x1
0000000 ad a0 0a
0000003
$ echo -e '\xad\xa0' | sed 's/\xad\xa0/\x20\x6e/g' | od -t x1
0000000 20 6e 0a
0000003
$ echo -e '\xad\xa0' | sed 's/\xad\xa0/\x20\x6e/g'
 n
$ 

Regards.