How to Connect Headphones to a SMSL DAC

I use my NODE 3 N130 with a SMSL M400 DAC.  The NODE has a 3.5mm headphone jack, but it bypasses the SMSL.  The SMSL does not have a jack,

On the SMSL the RCA connectors are used for the powered speakers, and the XLR connectors are used for two powered subs.  I still have optical, HDMI and Bluetooth outputs.

I’m thinking of Sennheiser HD600 or similar headphones, but I don’t know how to connect them to the DAC.  Any thoughts are appreciated.