Indeed the audio card only connects to the main board via USB. Here's a picture from the unit I used to have that might help.

[Linked Image from hifi-advice.com]

Rowland Model6/BPS6, Rowland Coherence II, Levinson 390S and 37, AudioAanZee Reference Flow music server, Rowland Aeris DAC, Rowland Cadence phono stage, Pass Labs Xono phono stage, Yamaha PX-2 and Thorens TD 160MKII, Transparent Ultra and Reference cables, Apogee Diva magnetostatics (refurbished).