It does sound rough, although I have no idea of which kind of roughness the TM likes :)
If sounds give a thread life, let's post some more... I have been fiddling with Guitar Rig, a piece of software that I own and has several filters implemented. In particular, it has something called "Formant Filter", and I had no idea of what that was until I read this thread, but now I know it's related with trying to imitate the sound of vowels. It also has something called "Talk Wah".
Here are some versions of Vocalise that I have just played with my EW plus, with and without these filters. Sorry for the bad playing (even worse after listening to Peter's), it's just so that anyone interested can see what these filters do:
* 1. My normal setup: EW + EHX Holy Grail Plus (physical) reverb: vocalise1-standard.mp3
* 2. Played one octave lower, and with EW + Guitar Rig's Formant Filter + Guitar Rig's Spring Reverb: vocalise2-bass-formant.mp3
* 3. Played in the same octave as 1, with EW + Guitar Rig's Formant Filter + Guitar Rig's Spring Reverb: vocalise3-standard-formant.mp3
* 4. Played one octave lower, with EW + Guitar Rig's Talk Wah + Guitar Rig's Formant Filter + Guitar Rig's Spring Reverb: vocalise4-bass-doublefilter.mp3
* 5. Played one octave lower, with my normal setup: EW + EHX Holy Grail Plus (physical) reverb: vocalise5-bass.mp3
Obviously, these filters are not like the TM, but I think they are interesting. They do make the theremin sound more "organic". I quite like how 2 sounds (crappy playing aside). Not good enough that I would always prefer it to my normal setup, but for some pieces I could, for a change.
The problem is that the filters make the sound more human, but they make it like a human speaking in an old radio :) I don't know to what extent this is due to (1) Guitar Rig's filters being worse than the TM's, to (2) the EW output not being "harsh" enough for these filters, to (3) not having found the combination of knob positions in the filters and the theremin itself that will give the best results, and to (4) my playing.
By the way, Guitar Rig also has distortion modules, but I haven't been able to get anything good by placing them before the formant filter as suggested before. I just get a more distorted result. I guess they are not the right kind of distortion...
PS: the backing track is the one that terrymin uploaded to these forums: http://www.thereminworld.com/Forums/T/24529/vocalise-backing-track