Totem Arro and Totem Sttaf are good choices for small floor standers. They match well with Naim. Surprising bass from such a small footprint. Sttaf's are easier to drive, but also harder to find used. They are a step up from the Arro.
With the 5i-2 you do not need to use Naim cables. Older models were designed to expect the impendence of their cables, but that is not the way the amps are designed anymore. So, pretty much anything goes, although lots of people still use their cables.