Good question. Since I'm having to rely on memory, my assessment may not be 100% on the mark. That said, here's what I recall:
The Dayens upgraded Ampino @ $672 USD
Overall, the upgraded Ampino features a more versatile performance envelope. It's larger power supply gives its presentation more weight and drive. This beefier power supply also results in stronger bass that will sound more consistent across a wide array of loudspeakers. The midrange is more colored sounding than the Sparks - erring slightly further into the warm and thick side of the tonal spectrum. Otherwise, the top-end and imaging sounds more or less similar.
The Vista Audio Spark @ $350 USD
The Spark by contrast, features a more balanced and neutral sounding midrange. The integration between the major frequency brands strikes me as a touch superior, and the noise floor on the Spark is notably lower. No, it won't have the muscular presence of the upgraded Ampino (or even the regular Ampino for that matter), but I nonetheless feel like the Spark makes an excellent showing for itself at nearly half the cost.