Output amplitute from an NCO

I am sorry I can't run any projects at the time being.

I suggest the easiest way is to use nios or signaltap(or simulation) after adding this simple piece of code on your sine data:

-- get max data
process(clear,clk)
begin
if clear = '1' then
    temp <= (others => '0');
elsif rising_edge(clk) then
    if temp < data then
        temp <= data;
    end if;
end if;
end process;

you can use nios to clear temp or read its value per each frequency.

Remember to make temp and data signed type