Do you mean active speakers? If yes, then you can easily connect them. If you mean passive speakers, it depends a bit on their sensitivity, but the headphone output would not really have the power to drive any speakers properly. For passive speakers you need a power amplifier. How powerful that amplifier would need to be depends on the speakers' sensitivity and the listening level that you require. I drive my inefficient Harbeth P3ESR desktop speakers with a refurbished 2x100 watt Quad 405-2 power amplifier, and they like the power. I am deeply convinced that for realistic sound power is very important - the more the better. The good news is that these days watts are cheap (unless you fall for audiophile nonsense).
RME ADI-2 DAC fs, Quad 606-2 power amp, Quad 2805 speakers, B&W PV1d sub with Antimode 8033 Cinema