(link is for windows version), and select RC5 protocl, D=16, leave S empty, and enter in, for example, 17 for volume down, or 56 for mute off, or 1 for the digit 1. Click Render to see the Pronto Hex.
BTW, your post would have been much more readable if you had troubled to manually insert spaces instead of allowing everything to run together.
"Mute off5638*" is interpreted as function 56, or equivalently function 38 (hexadecimal), and I don't see anything that tells us what * means.
RC5 uses a toggle bit, so the long presses may not work. We can try a different Pronto Hex for the long presses if they don't work.