Hi GTFOOH,
Two ways - either connect some speakers via the optical cable
(e.g. http://www.amazon.co.uk/Logitech-Z-906-Surround-Sound-Speakers/dp/B004MY4PU6 - which is the successor to the awesome Z5500 which are my speakers)
OR
thread the HDMI out of the PS4 to a dedicated amp, which will...