[exray]

Aha, yes I now see C1. Another case of being specced for leakage rather than voltage. RCA was GOOD (bad) for that!
630vdc cap will be fine. 50v disc would be fine for that matter

The only critical one here voltage-wise is C11. As I said, 630 may go forever but to explain the "correct" thing you may want to consider going higher. There can be some very high audio AC spikes during thundercrashes, etc. In the old days that meant a shorted paper cap which in turn could take out the audio transformer. Modern caps are much more resilient. If a strong spike were to 'punch thru' a layer of dielectric they will self-heal and clear any short. I (and others) have played with these caps and they really do what they say. I once drilled multiple holes in one in this location and couldn't make it short out!

If you want to be 100% safe you could use two .047/630v in series. That would give you .023 @ 1260 volts and you'd never have to give it a second thought! Or, .02@1000 vdc isn't hard to find in a ceramic disc capacitor if you're shopping anyway.