Hi Andrew, and welcome to Beoworld
You also need to have the ground lead from the sleeve of the DIN to the earth contact on your amp, otherwise you will get terrible hum.
I've seen these for sale but unfortunately can't suggest any particular place. If you can't find one, you can temporarily use a separate jump wire from the amp earth and stick the other end between the sleeves of the DIN connectors. Should work well enough until you find a suitable adapter.
Oh yes, the adapter also needs to be from the DIN to the RCAs - these dual RCA adapters are directional, since the DIN has stereo connections both ways. For this reason, I always buy DIN to 4 RCA -adapters, the two extra RCAs possibly hanging free won't do any harm.