I have told him focus on speakers first, then source components.Focusing on speakers first and then finding an amp to properly drive them is a generally sound advice but in this case, an A21 will pretty much drive any speaker he is likely to fall in love with. He’ll be fine.
The JC2 preamp and JC3 phono stage will handle any source he will be looking at after the fact.
That notwithstanding, is the "All Parasound " a good idea to avoid the possibility of components not playing nice together or should he not focus on brand loyalty and shop for "best in class" components instead?Sure, why not. He is guaranteed that the components will be properly matched to one another both sonically and aesthetically.
Sound like it will be an awesome system. Give him a thumbs up and enjoy his system when you go to his place.