The Arcam would be the better choice in longer term. Though initial listening with the NAD confirms its taut bass delivery vs NAD, the "midrange magic" is undoubtedly with the Arcam. And upgrading to power cords like using the silver audio powerburst is most helpful with these Brit amps. Significant gains are aplenty with the Arcam than the NAD. For some reason some super value cords like the Synergistic Master coupler while it matches well with most hi end territory separate preamps -amps, it doesn't do as well as the powerburst.
The reason why I emphasize this is that power cords are integral with the amps and it is not often that you change it as much as interconnect cables. And when you start switching in between various cables, it makes sense thinking that nothing else from above the chain spoils your subjective listening.