I would think that REL might be a better match, the puppies will play considerably louder the the REL but with the 63s that is irrelevant. with either keep the crossover as low as possible. My speakers have around the same bass extension as the 63s [I sold them both at the same time] and I cross the RELs in the 25Hz area, bringing them up and letting the main speakers run full range. The Quads are so revealing that I have always been able to hear the crossover when I ran the signal through it.
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