There is a whole world of great sound quality out there to explore. It can be intimidating and pretty easy to make a wrong first moves.
First the landscape. Moving out of Marantz is a great first step. There are a couple long term reliable… built to sound great budget brands: NAD and Rotel. These are a step out of consumer offering. Reliable, good sounding, and built like tanks, lots of reviews, long histories. Then there is Schiit… yes really. This is a great budget “high end” entry brand. Also, highly reviewed and excellent value for the money. Alternatively there are many many boutique brands like the one you are looking at. They can be great value for the money. There is risks of good performance of some characteristics and not so much in others, the brand might not be there in a few years, reliability could be an issue. I am not saying any of these are true with Heaven, I don’t know. Any way consider NAD, Rotel, and Schiit, as a first step into higher end electronics. On the other hand Heaven could be a great choice.