Dear Juan,
Early polyphony does indeed fascinate me, but (not being a musicologist, and given the transience of non-written music) I wonder how much we misattribute 'firsts': what would Charlemagne really have heard at court?
I've only heard one BBC radio programme on Leonin and Perotin, whom I recalled as pretty much contemporaries of Hildegard of Bingen, though I found out on checking that I had remembered the probable date of her birth (1098) as the date of her death (which was in fact 1179), so yes, I guess they were at least a century earlier. The renditions I heard were not especially good ones though. I shall have to try harder.
The trouble with modern music is, I always need a run-up. I can now listen to Ligeti with considerable pleasure, but it took me a while. Stockhausen, on the other hand, has always struck me as over-intellectuallized and not really musical. And I like modern re-interpretations of slightly less modern music such as Tomita's version of Pictures from an Exhibition, which is one of the few albums of purely instrumental music (no words) that can reliably make me laugh out loud.
On the other had, a couple of years ago, I heard a young woman singing "I will show you hidden things/Hidden things you have not known" (? Isaiah 48:6) as a mantra, the words unchanging, the music and stress varying. This was an entirely modern rendering, as far as I know, but I have never been able to find it again. Can you or anyone else point me in the right direction?
Emma Kirkby is indeed wonderful, though I have to say that in her recent BBC programme on the lute ('Luting the past') I preferred the lute music and Emma's voice separately rather than together.
Monteverdi is a bit twiddly for my taste, though not as bad as Mozart. A friend of my brother's once said, "Anything after Mozart is film music" but I find Mozart over-ornamented (heresy I know). If you're going to do that sort of thing, do it properly with a battering ram: Beethoven's "Consecration of the House", for example. Most early music is both minimalist and richly textured, and it seems to me that anything after, well, maybe Purcell, lost texture with over-enrichment. Even Purcell lost it half the time.
Cheers,
R.