To me it's the combination of the digital front end and the analog filters that does it... not any of them stand alone... I honestly have no interest in the digital engine alone because it has the typical Waldorf digital sound to it which is rather sterile and well... digital... I've always liked Waldorfs hybrid and analog products, but really none of their 100% digital ones...
I'm discovering I like hybrids most of all. (Though I'd still like a flagship analog poly, but that's a different quandary.)
Along those lines, I really liked the video I think maybe loopop did of just going through the presets of the Minilogue XD: it was really impressive and I liked it more than the Prologue demos--I think possibly because they improved the filter. Pity it's only 4 voices, but the price makes me less leery of it than the Prologue.
I'm still not sure it's what I want right now, but it does seem to have a very wide sweet spot and some great, full-sounding sounds.