Alright, I've actually stumbled across it just now while playing around with some presets.
However its using a strange waveform in Zeta+ so wouldn't know how to explain it to others - but I think it's effectively detuned triangles with a bit filter on the top to take the crispy highs out and you end up with the soft synth sound
I see you found something while I was typing but here's my thought's on it:
They're chords(or just two notes), so you'd have to multitrack the Micro, but it's certainly possible. Use portamento and turn the cutoff down to get that muted sound(or just use a sine/triangle wave). Legato will keep the envelopes from retriggering, as well. The clip is probably done with a "chord memory" function. Many synths have this. Multiple keys can be triggered using a single key. This takes polyphony. If the synth has poly portamento, it would just be a matter of playing chords with legato.
Come to think of it, if it's only two notes, it may just be a 2 Osc synth with the tuning to the desired interval.