Tiger eyes would be a great combination. I have a Tiger Eyes next to a Black Beauty sambucus. The Black Lace, if it gets a fair amt of moisture, is vigorous, grows "like a weed." If you want to combine it with another Sambucus, "Sutherland Gold" is a bright yellow chartreuse, and "Pulverenata" is mottled with white flecks if you want that combination.

Interesting the very different experiences folks are having with this shrub. So I thought I would add my two cents from Toronto. I have two in my front garden (one of either side of the front walk), which is part sun and clay soil with lots of organic content. And they are excellent. I keep them relatively small with regular pinching, but I let them go a bit this Spring so I would get flowers and there are dozens on each shrub (still only about three inches across but growing everyday). They are bullet-proof and vigorous, for me, and their colour and form and highly dissected leaves are not easily replaceable. I have them with (among others) Liberty hosta, pincushion boxwood, Rozanne Geranium, Jack Frost Brunnera, Full Moon Maple, Krossa Regal and Blue Mammoth hostas, and Incrediball hydrangeas. I love the mix but it would be boring without the contrast this shrub brings, which makes everything around it pop. If I can figure out how to post pictures someday, I will.

That's weird, because we have issues with elderberry (z7) not liking the heat...well maybe winter hardiness zones have little to do with heat zones. I must remember that ;) However, I find elderberries to be tough customers and I would bet that a strong plant will do just fine. Even if pruned to ground, they can get five feet and flower in a single year (I think I remember this and am not making up from whole cloth).

For the turk's cap: I'm looking for the Texas version (drummondii), that has broad leaves and edible fruit.