Does it not have any other inputs? As you won't actually be getting true surround sound with that setup, just emulated surround sound from the stereo input.
If that's the only option, then something like spiderplant's link (Although you can find the lead much cheaper) is your best bet to take the stereo sound from the scart socket. It's pointless buying an adapter to convert the optical output to stereo because you'll end up paying way more for the adapter than you could get a scart lead for.
One of these on the VCR scart and then your existing phono jacks will work fine. Just make sure if you do go the scart route you want an OUT and not an IN, or you want it to be switchable.