Cable from your LAB599 TX-500 radio (REM/DATA 7 pin connector)
To our RBI-1 interface 
Connect RBI-1 output to whatever amplifier you wish (*RBI-1 RCA jack output has closure of contacts, contact to ground) 

NOTE: We also make a cable and interface solution from your LAB599 TX-500 to Xiegu XPA-125B and other amplifiers in a separate listing at   https://www.ebay.com/itm/324942541844