There are a number of threads here on houzz.com that discuss high velocity systems such as Unico and Spacepak. Just do a search in "discussions" and you should find a number of them.
Before committing to any forced-air system, be sure to explore ductless mini-split heat pumps as an option. The are well suited for retrofit applications, have high efficiencies, good turndown and eliminate a number of problems that come with pushing air around a home.
Q