The problem with any sort of "blocks of functionality" approach or even "field up-gradable" type design is that costs end up spiraling AND the base of potential users / buyers SHRINKS. The fact is even really nicely made solutions from firms like NAD carry costs for the "cards" alone that greatly exceed the cost of entire AV receivers from other makers. https://www.crutchfield.com/fg_370450_FFBrand%7cNAD/NAD-Add-on-Modules.html vs https://www.crutchfield.com/p_033AVX1300/Denon-AVR-X1300W.html

It is not a stretch to suggest that these sorts of issues are not limited to smaller manufacturers but are also seen when one looks at the product offered by the "big guys" too -- especially when considering things that are a bit "mainstream" compared to generic AV receivers it becomes apparent that design & component costs tend to create a "floor price" -- compare what Yamaha charges for something like the two channel integrated amp / DAC / streamer: https://www.bestbuy.com/site/yamaha-musiccast-wxc-50-streaming-media-player-dark-silver/5688016.p

These sorts of market realities have certainly driven the collapse of Pioneer's home audio business, and forced many mergers, especially between firms like Marantz and Denon that otherwise had extreme overlap in their offerings.

The extreme flip-side shows that there has been an explosion of firms offering extremely "no frills" alternative devices that can be used as either stand-alone products with minimally "open" digital audio sources or turned into a chain of Rube Goldberg type solutions. It is not realistic to expect Outlaw, Emotiva, or any other firm that has had success as a value-oriented option for "normal" AV users to compete with such things -- https://www.parts-express.com/Search.aspx?keyword=dac&sitesearch=true