Sorry to have come into this thread so very late: I'm just returning to the forums after several weeks.
We have a weekly Zazen session at my school, and moreover, the Austin Zen Center is not far from me. However, I have to say that it's not very easy. My natural tendency is to attune myself to what's going on around me, not to block it out.
Last year, I took a kundalini yoga class, and found myself developing an almost radar-like sense of awareness: now THAT, I can use in aikido!
I'm curious about how to blend the two disciplines now.....
Zazen (shikantaza) expands awareness, eyes open, allowing thoughts to come and go, without holding on to thoughts, while maintaining full breathing and balanced posture.
Kundalini yoga sounds interesting.