Perhaps you should stop using THD as the deciding factor. I haven't paid attention to it since the 1970's.
Soix is correct. You need to invest in a modern AVR and use it as a hub for all the components. Personally, I use Anthem, but there are many options. What I would recommend is that if you do upgrade, make sure the AVR has the capability to output the front channels independently. This will allow you to integrate a two channel system with a home theatre bypass option sometime in the future when you get the itch for a better musical experience.