It sure the heck is a swl forum, and it also pertains to hams! (EHAM.NET). Read further into the link and it tells you what features the tx500 has that will enable you to receive on the gear that you already have. If a 500 kHz receiver is not available, you can switch ON the built-in high dynamic RX up-converter and listen to the 500 kHz band with a 3.5 MHz receiver.
If you don't like to buy a kit, then use the schematics and build your own up converter and band pass filters. With the kit, all of the math has been figured out for you so you dont have to brew your own.
Robert KH2BR