Great information thank you kindly.
The piano forte lives in the house, and it’s really fun to hear the performer practicing all the time on it. Really neat. two years ago I recorded a mini concert with 2 baroque era cellos and piano forte there with an all baroque program. It was lovely.
Do you have an external 2ch preamp (to record ch.5/6 on the MixPre-6) or an extra 2ch recorder plus a pair of mics? If I were setting this up, I would want the two pairs you described, plus I would also set up mains, assuming nobody minds a tripod in the way. I'm an amateur, not a pro AE, so you can take what I say with a grain of salt. However, I record a lot of pianos in conductors' living rooms. For mains, I usually run A/B array (12" or 16"), as I don't personally see the sense in ORTF/NOS/DIN/whatever in a living room (you'd just be inviting more wall sounds). I try to put the tripod on a carpet (less floor bounce) and depending on how it sounds I like a wide cardioid for this. If the room sounds bad, then you can do hypers or even a Faulkner Array (pair of Fig 8's in A/B) to take the room sound out. As you know, if there is a wall behind the piano, you will still get a lot of muddy wall reflections off of this back wall. Sometimes aiming the mains at an angle helps (A/B mics -> piano -> corner of the room in a line).
The idea is that, if you want to do some nice mixing with your two pairs of spots that are right on the instrument, then you'll likely get the best tape, and you can make it sound more like a concert hall than a living room if you have mixing skills and a nice reverb plugin (or box). However, a pair of hard-panned A/B mains means you can have an 'instant mix' ready to go on the spot. It will sound...a lot like what the audience in the living room actually hears.
One last tip. Nobody does this, but I personally *love* M/S arrays on classical concerts in living rooms, both as spot (stereo) mics and as mains. The reason is simple...M is the standard spot, and the S lets you dial up/down the amount of wall reflections you hear. In the absence of added reverb/processing, my best living room piano tapes are M/S, since I get to choose how much of the walls I want to hear.
Again, just some thoughts from someone who does this a fair bit on a very non-professional basis (usually with 10 mins max setup time and zero sound checks because classical musicians around me all seem to agree that good recordings are made by putting up a microphone and hitting the red 'on' button)