Put one EV-666 down every sound hole, run them through vintage DuKane, or Bogan, mic pres. Make sure it has a bad transformer and leaky caps. Just a "touch" of compression from a Gates leveling comp, and a smidgen of EQ from a White 1/6 octave graphic, make sure every knob is turned. Then pan all mics to give the most spead. For reverb, a vintage Master Mix spring reverb works wonders. Voila'! ;-)
Seriously, it does depend on the type of music, what role the piano plays in the total scheme of things, lead or backing rhythm. I've used many different mic placements, spaced pair, XY, low / high, over the hammers, inside, outside, etc... Stick your head in there and listen...
I love an AKG C-24, (I love a single point stereo mic) or pair of C-12s when I can get them, Sanken cu-41, AKG 414, there are so many that work, really. With the freq. response of most of the Chinese line of mics you don't need eq.
We used a pair of U-87s with Milsap's CF-III 9', one over the low strings near the bridge, the over the high strings. That's the way he liked it and it worked. Board, Neve, pres, a little 3K and 10K. No comp.
The player's touch really helps. Room plays a big part, (I love Mark Burchfield's new place!)
Basically I try not to do too much so I don't screw it up!
I recorded piano yesterday with my x15 directly in the middle, placed flat, and hung two C12's outside the lid. Tried them in a dozen places before deciding. I can't say I achieved the sound I wanted yet. Maybe gotta work out some of the phase a little. I would have preferred to have it perfect before tracking. But I'm having to learn how to mic my piano in my room. It's been 15 years since I'd tracked real piano. Ugh. Hate admitting that. The sets of mics didn't work well together on phase, but each set independently sounds great. We'll see.
you should try it the other way around... seriously. And back the x-15 off a bit to minimize the phase. It's having them relatively close that makes the more pronounced phase effect... but the room tone needs to have a good character about it or you could be out of luck. I am assuming you are using 4 tracks and not combining...because I would certainly want to be able to adjust the relationship later.
At that point it would be more prudent to go with a single pair miced close
How'd you get that big ole grand up on the second floor anyway? I am sure you'll get it. You've got a good ear and you're a good player. Like you, I try different placements and mics. I have found a couple of ways that sound good. We have a Baldwin 9 Foot that I put a C-12 and the end looking down the bass strings just outside and a TLM 103 over the highs near the hammers. This gives a good stereo spread. I also love to put a pair of 414's in an ORTF about head high in the bend, just over the edge of the piano (with the lid fully open). When I stand there, it just sounds good. So, I just put the mics where my ears were. Some times I do both and just blend them until I get the sound that works in the mix. I use the pre's on the Neve and no compression until the mix.
As far as brightness, one trick is to press the "soft" pedal slightly to offset the hammers to where the felt is softer and that "warms up" the tone.
Hang in there and you'll find the right combo.