There is two ways to do it :
For wire - connect your iPhone 5 earphone jack with iPod HiFi (at the back of it / audio in) with a 3.5mm cable
For wireless, you need an apple tv, and connect your apple tv with iPod HiFi (at the back of it / audio in) with a optical cable
You just need to buy "Apple Lighting to 30-pin Adapter" to make all your odl accessories work with your iPhone (including iPod Hi-Fi).
iPod HiFi launched before iPhone, therefore if I can remember, you can play iPhone on its dock (HiFi) but it can't be charged, as iPod HiFi charges through the Firewire pin which is no longer supported on the iPhone. Therefore, the lightning pin adapter may work but you may see the error message