As for the M-Audio C03, I don't find it in their product line.
I think it may be discontinued, but there is stock hanging around in some places.
Anyway there are other products out there that provide the same conversion, so that's good.
You need to make sure that whatever converter you choose doesn't add jitter; the CO3's has in-built jitter management (which I assume is a phase-locked loop like in the 518). It wouldn't be quite so critical if your Genelecs have jitter management themselves on their inputs, but Meridian has demonstrated time and again that digital stream jitter is the enemy to audio fidelity.