If you look at the AES plugs of your device, then you will find an AES input and an output plug.
Either XLR (1 AES port) or DB-25 format (4 AES ports).
Every AES I/O port carries a stereo signal compareable to SPDIF (only at a higher level, using symmetric cabling, with galvanic isolation / use of transformer and with other impedance).
What do you mean by bi-directional ?
An AES output sends digital audio in AES format to another device.
An AES input receives digital audio in AES format from another device.
Yes, you can use an AES port for connecting external effects.
BR Ramses - UFX III, 12Mic, XTC, ADI-2 Pro FS R BE, RayDAT, X10SRi-F, E5-1680v4, Win10Pro22H2, Cub14