It shouldn't be impossible - someone will know. There are a limited number of formats for these things. You'd need to find the make (like Molex?), the type, the size and whether you need some cripplingly expensive crimping tool to make it work.
It might well be you can get a couple of them off ebay for a few quid and use needle nose pliers to attach the crimp terminals. I'd have thought they would be somewhere in the technical documents for the preamp, or someone on a Yamah specific forum could tell you the exact model number etc.