Sorry... I was not familiar with the Domino and I thought it was just an oscillator. From what I can tell it IS a synth voice.
We can work with that. So your synth voice is going to need gates to trigger the VCA and will need pitch information via CV plugged into the 1v/OCT jack. That's the basic requirement to get a pitched note from the synth. From the look of it, the only envelope parameter available is the decay time. Other synth voices have more options but also a heftier price.
If you're into DIY electronics, check out the Ornaments & Crime and Temps Utile. You can build the micro versions yourself and save a lot of cash. Between those modules you'll have a TON of functionality in 16HP and won't need the Steppy or the Scales (at first). Throw in a Disting for $200 and betwen those three you have a nice system for modulation, clocks, light sequencing, etc.