With this logic @ghdprentice then we should all dump our separates and get an All In One?
Also AR is not the end all be all, matter of fact there are many DACs that are much much better. Bit of an AR homer.
If you are in the market for a better DAC, I recommend that you do just that. Introducing additional components like a tube buffer also introduces another component and set of interconnects, with their associated signal degradation. The best sounding solution, assuming equal quality components is the fewest. Also, I think the least expensive.