Thanks for getting back to me.
The Philips TV is an ancient model – 10+ years old – but I can let you know the model number later, if it’s any use. To be fair, it could probably do with upgrading!
I have been playing around with the ‘tink this week and found that Wii over component also works perfectly if passed through my AV receiver. I have tried NES through composite, and that does not provide audio whether direct to TV or through the receiver. A shame, because I think the ‘tink makes the NES look great! I have also tried my Laserdisc player, and that works fine (and also looks great), so I am satisfied this is just a NES issue, and not the composite input itself.
I have also had another go with my AOC monitor, and that now works fine. So I will assume user error on my part!
I will try a bunch more consoles tonight over composite, and also OG Xbox over component.