Using McCormack DNA-0.5 Deluxe as Mono Amps

I just did a horizontal bi-amping and was amazed as how good it sounds. My bi-amp-able speakers have high crossover at 3.5KHz. So I wasn't expecting much improvement on the bass/mid side but it improved dramatically, which I don't quite understand. Bass is louder, lower, and clearer than before. Vertical bi-amp does have the advantage of coherence and possibly shorter speaker cables. However, horizontal bi-amping, if done right, has the advantage that, inside the power amps, the high current of bass/mid cannot affect the delicate current of the highs, which I noticed a dramatic improvement. Anyone can enlighten as to why the bass/mid improved will be appreciated.

Anthing new or different now that 9 years have passed. I’ve got/had Revel studio 2, salon 2, B&W 802D3, and many amps ML 534, MC275 pair, MC601 pair- would anyone suggest some sort of biamp with all this type of gear or just use one set of amps at a time?