this is Petr Wagner calling!
My reasons for doing ZVW 176 in one-per-part seating were pretty straightforward:
1) as Bernhardt Blattmann writes in his booklet notes "...in a court church catalogue of works compiled in 1775, the collection [of the Italian Arias ZWV 176] is in fact listed as “Arie da camera”.
2) there are separate instrumental parts surviving for these arias (kept in Dresden archive, too) and there is no single sign that there were more copies that would at least suggest larger - orchestral seating. No wind parts in the score, either.
3) I think - and this is just my speculation - Zelenka might have actually arranged these pieces fairly quickly from a rather thin voice-and-continuo/harpsichord versions he had either composed in course of his later career or in course of just a couple of weeks. Who knows, really... However, 2 violins, viola and basso continuo seem to be the most logical last-minute and fast solution of arrangement of that kind of material.
4) I just love the light sound of small chamber group with voice in this music. The texture is transparent, not foggy as it happens with larger orchestral bodies, and it blends more naturally with the soloists' voices extremely well, without pushing them to dynamic extremes.
Anyway, I hope you enjoy ZVW 176 as much as I do!
Greetings from Prague,