nirun
2
you can plug the audio out from your modular directly into your OT, but you will have to watch your signal carefully- the audio can run really hot so with any VCA/attenuator/mixer module you should be able to manage the levels pretty easily to prevent clipping/bleed/distortion
For now I use the uJack from intellijel, nice little headphone amp with 1/4 inch line level outs http://www.intellijel.com/eurorack-modules/µjack/
No direct experience sending audio from OT, but I believe you will need to crank up the AMP on the OT with a snappy envelope to send triggers/clocks