Need Help With Desktop Audio System

So currently I'm using a old Sony stereo system that has no AUX jack plug as a imput to plug the PC into the unit and instead I'm using a cassette adapter (one of those ones with the 3.5mm headphone jack wire coming out of it) for getting the PC to hook up to the stereo system. Now I want to replace this system which is a very old system with somthing newer and will still allow me to use my 40watt AWIA speakers does anyone know of a little hub or audio unit that will allow me to hook up my pc to it using a 3.5mm headphone wire and will be able to power my 40 watt speakers that use this connector

I got one of these back in December to power 2 Infinity speakers and 8" powered subwoofer for my desktop. Works great. I got mine on Amazon but they aren't available there anymore.

Edit: use a 3.5mm to RCA cable to go from the PC audio to the desktop amp.