Have you considered installing track on the top side of the beam

Talk to a lighting designer, someone who knows their stuff.

Here is a good looking lighting for a vaulted ceiling. Check out the questions and comments on the page which might be helpful.

If the only purpose of the lighting is to illuminate the vault then I would suggest that you look at LED lights mounted to the top of the beam. You can get strips (even wash of light) or pin lights (pools of light) depending on the look that you are after. I would try and avoid dropping any fixtures in the space as this will compete with the simplicity and beauty of the trusses.

We had originally purchased the track lighting for our kitchen but we ended up having enough light with the 3 can lights and 4 pendants over the island, lighting on the stove and under cabinet lighting.
Basically we were oversold additional $ 3K of lighting. So we are trying to make it work.

I'm not sure how the track lighting would look with the standoffs and the 3 " inch light extensions.

I'm too am concerned about how the ceiling will look