Sorry, it won’t work, as HiFiman says. If you want a separate DAC in a Naim system, you need a full separates setup, as once you use the digital output, you cannot route the signal back into the analogue side of the same box. This applies to any of the all-in-one boxes.
Some DACs have a digital volume control or preamp built in, in which case it may be possible to use it straight into the power amp, but in Naim systems that doesn’t always sound that great, and most of the 272 then becomes redundant.