How to evaluate CD DAC vs. outboard DAC quality

I have a Cambridge Audio Azur 840C CDP that received positive reviews upon is release. If, as I keep reading, DACs have advanced by leaps and bounds over the past several years, I have to wonder if adding an outboard DAC would improve the overall sound quality. My audio goal is always the same: greater musical realism!

So the question is: How can you know whether a recently released DAC (say around $1000-$1500) will be a useful add-on? I'm not looking for the flippant and unhelpful try-it-for-yourself-and-see response. I'd genuinely like to know A) whether modern-day DACs really are superior to those from five or ten years ago, and B) whether someone with a large CD collection and no interest in computer audio is better off forgetting about a DAC and investing instead in a better CDP, like Ayon or the like.

Thanks!