Please see my Neco.
https://us.diablo3.com/en/profile/NatureBoy-2690/hero/122703413
He is having a Tals Amour Primal Ancient.
let’s say if I where to switch to Aquila Ancient , Do i gain another 375% in damage and 2% reduction from Legacy of Dreams?
The tals Amour attack speed and stats from Primal Ancient is great but… which set up is better?
Huh? Primal ancient pieces are ancient for LoN purposes.
if i replace the tals chest, and replace with Aquila , do I get additional 375% form LON gem? thanks
No. An ancient Aquila gives you the same bonus that a primal ancient Tal chest gives you from LoD.
Thanks for your help 
Also, you don’t want to look at it in isolation. A lot of people see that big 375% number and think “wow, that’s huge!”. But if you already have 12 ancients, adding a 13th isn’t a ton more damage from the LoD bonus.
Going from 12 to 13 ancients increases the LoD bonus from 9375% to 9750%, which is effectively about a 4% DPS increase. And it will increase the damage reduction from 50% to 52%, which will increase your toughness by around 4% as well.
But as Khord pointed out, ancients and primals both give the same bonus for LoD. So it won’t make any difference for you, except you’ll lose the attack speed from Tal’s and gain the affix from Aquila.
If you are very good at keeping your essence tank not full, then you will get no benefit from Aquila. Personally I like having the Aquila. In many cases when I swing my scythe and hit multiple things, my essence goes up to full in milliseconds so before I dump it there is small time window I stay with full essence. Obviously if I was a better player, the tal chest would benefit me more. As the others said, ancients and primals contribute exactly the same to the legacy of dreams gem.
I am wondering , there can only be one at a time , that Aquila and the shoulder piece is active. I am thinking isn’t that a waste. When one ability is active, the other does not. that makes me think if the shoulder or chest can be replaced with something else
Yes only one of them can be active. That’s why the chest piece can be talrasha. By having both Aquila and Razeths you have that 50% reduction up all the time, so it is a more lazy setup when you can walk in and out of groups of enemies with one less thing to worry. I know that for myself I cannot play for let’s say three hours and always keep an eye out for my essence to not be full. I know that I 'll screw up eventually so I use Aquila more as a failsafe. If you are noticing that you die often because you get caught with full essence, you either need to be emptying you essence more frequently, or you could just use Aquila and forget about it once and for all.