Since the pianos are different, I would try to make a similar tonal balance, first. The instrument with more projected sound put as a 'front' one. Since you will probably need a distant micing, let 6-10 feet between the pianos. Listen to the instruments and try to decide which one has brighter or darker sound. With brighter piano place your mic closer to the bass strings side, with darker, to the highs. Also, try to tilt the mics towards strings for less projected instrument, and open lid, for more projected one. In short, with micing try to equilze the sound as close as it is possible, then take care of the rest with EQ. Actually, for the close mics I would try your SD cardioids first, and use omni pair with 4033 center mixed to two tracks, as a room reverberation, but you will need to experiment.
Of course, the pianos should be tuned against each other, otherwise it will sound like... J.Cage 1/4 tone pieces. But I am sure you know that.