You can just connect the Hugo RCA analogue out to the 272. Naim amps generally prefer DIN connections, but if you have an RCA-RCA cable it will still work fine.
I’m not familiar with the Soundkey, but the Hugo is a very capable DAC, so it should be a nice upgrade.
Why not connect the iPhone directly to the 272 via the front USB? There’s a trick… you have to first play an album in iTunes, then select your streaming app. No need for extra cables or an external DAC. I listen to hi-rez Qobuz on my 172 preamp via my iPhone. Sounds great.