Hi there! I have 2x Logitech F710s which have the same buttons, so I’m in the same camp as you.

You’re right in that defining a PSX-specific retroarch.cfg will override any settings you define just for PSX.

Here’s my /PSX/retroarch.cfg. You may be able to copy-paste it directly, as I bet your button layout is the same.

#include "/opt/retropie/configs/all/retroarch.cfg"
# All settings made here will override the global settings for the current emulator core
input_remapping_directory = /opt/retropie/configs/psx/
rewind_enable = false

input_player1_joypad_index = "0"
input_player1_b_btn = "1"
input_player1_y_btn = "0"
input_player1_a_btn = "2"
input_player1_x_btn = "3"
input_player1_l_btn = "4"
input_player1_r_btn = "5"
input_player1_l2_axis = "+2"
input_player1_r2_axis = "+5"
input_player1_l3_btn = "9"
input_player1_r3_btn = "10"
input_player1_l_x_plus_btn = "h0right"
input_player1_l_x_minus_btn = "h0left"
input_player1_l_y_plus_btn = "h0down"
input_player1_l_y_minus_btn = "h0up"
input_player1_r_x_plus_axis = "+3"
input_player1_r_x_minus_axis = "-3"
input_player1_r_y_plus_axis = "+4"
input_player1_r_y_minus_axis = "-4"

input_player2_joypad_index = "1"
input_player2_b_btn = "1"
input_player2_y_btn = "0"
input_player2_a_btn = "2"
input_player2_x_btn = "3"
input_player2_l_btn = "4"
input_player2_r_btn = "5"
input_player2_l2_axis = "+2"
input_player2_r2_axis = "+5"
input_player2_l3_btn = "9"
input_player2_r3_btn = "10"
input_player2_l_x_plus_btn = "h0right"
input_player2_l_x_minus_btn = "h0left"
input_player2_l_y_plus_btn = "h0down"
input_player2_l_y_minus_btn = "h0up"
input_player2_r_x_plus_axis = "+3"
input_player2_r_x_minus_axis = "-3"
input_player2_r_y_plus_axis = "+4"
input_player2_r_y_minus_axis = "-4"