As someone who went from the La Voce to La Scala, I would say that the difference isn’t night-and-day: both are superb, arguably reference or world-class dacs, and the La Scala has a bit more warmth and depth with its valve stage. Also I’d say the associated equipment - amp and speakers especially, make a difference, so that the La Voce would complement a valve amp and smoother organic speakers such as Harbeths well, the La Scala could perhaps balance a typical solid-state amp nicely - but these are of course generalisations.
I found the step from a very highly rated (non R2R) dac to the La Voce much greater than the change from the La Voce to La Scala. It’s probably worth looking at the owners’ Aqua thread on here, as well as checking out reviews. This La Voce dac is exceptional value.