I've just downloaded a copy of u-he's new analogue emulating soft synth, Diva. In the half hour I've played with it it seems a fantastic fit with the Eigenharp. I've got it running in multi-core mode and high quality (on a quad core 2.3Ghz Macbook Pro with 8GB RAM), hosted as a VST in EigenD and it's sounding amazing. There are some really nice warm and percussive sounds in there that work brilliantly with the Eigenharp keys and strip controllers. There's a demo version that you can download and it works fully, but just inserts white noise every now and then; I'd strongly recommend anyone on here to have a play.
For some reason the AU version doesn't fire up in EigenD for me, but the VST version works great.