Days report, for those interested ;)
The room was really quite small, but such an unusual shape the normal room modes were just not the problem. The double height hall (as it was a hall) had almost no parallel walls, balconies on three sides and a domed roof!! Listening around the space, the piano sounded great wherever, which was the bit I was really worried about. The mics went up in various positions while the pair played, including over the balcony looking down which gave a nice balance. The best balance was mics 2m high behind the flute pointing down ish, almost the ideal flute position, and placing her in the curve of the piano the mics could 'see' the strings. This gave a central flute impression, with a broad piano that had no issues when collapsed to mono :) This height was at the bottom of the balcony, so I put duvet over the balconies behind the mics and the other side where they pointed, just to cut first reflections.
However, this close to the flautist key clicks became an issue. The pads of the flute were pretty worn, and we ended up using about a pack of cigarette papers under the keys and moving the mics around to almost behind her head just so the clicks weren't so direct.
At this point I ran secondary spot mics to the piano and flute, pointing 180degrees away from each other so one saw the piano strings and one looked at the flute headpiece (again, slightly away from the keys). The thought of this was if I could use a 'transient designer' plugin to reduce the 'attack' of the flute (i.e. the clicks) I could support the main pair and at least minimise the impression of clicks.
We then ran through the pieces (2 sonatas, 3 movements each), and I was so grateful that I could follow the score!! After the first couple of recordings (where I was so busy monitoring recording levels and making sure I wasn't in loop record(!!!) I wasn't able to do anything else) I was able to note the score as we went through and make sure the mistakes in the next take were in a different place :)
I spent yesterday comping the different takes together, just from the stereo pair. Good news is that the key clicks are a lot less obvious over speakers than on my headphones. I've not tried the spot mics yet, bar a quick listen which has done nothing but confuse me. The piano is about the same level in each of the mics (did I mention this was a diffuse environment!), and the flute is not to far off. Either that, or I have the worlds only omni SE1a mics....
Big thanks for all the advice here. Notes on the score were essential. Main pair and spots was exactly the way to go. A pre-run would have highlighted the flute key issue (the flautist left slightly ashen faced after playback on headphones), but I didn't have that luxury.
We didn't record any solo flute pieces, but have agreed to do those at my place once the flute is serviced.
Other things: next time I'll get a long headphone extension lead to listen to the mics as I place them (I could only do that in a limited point from the pc, but it was bloody useful for making the image central!), and when listening to recordings of different positions, remember to normalise them first. I spent half an hour fine tuning an over the balcony position that only really sounded better because of a level difference!!
Now, hopefully I'll see you on the mixing forum as I try not to over-cook some basically good recordings!! I will post some of the comped stuff 'dry' and after a bit of hall reverb, for comment. Cheers,