As you probably know, an NRPN message uses two bytes to identify the parameter that it controls. The first byte is the Most Significant Byte and the second is the Least Significant Byte.
Therefore NRPN messages 0 to 127 are given by having the value of the Most Significant Byte be 0 and the value of the Least Significant Byte be in the range from 0 to 127.
NRPN messages 128 to 255 are given by having the value of the Most Significant Byte be 1 and the value of the Least Significant Byte be in the range from 0 to 127.
… and so on. It should be easy to figure out what values of MSB and LSB result in the NRPN for a particular parameter.
The AS-1 responds to NRPN messages in the range from 0 to 1152.
As examples:
NRPN 0 is given by MSB = 0 and LSB = 0.
NRPN 167 is given by MSB = 1 and LSB = 39.
NRPN 1024 is given by MSB = 8 and LSB = 0.
NRPN 1075 is given by MSB = 8 and LSB = 51.
NRPN 1152 is given by MSB = 9 and LSB = 0.