I started off shrimp keeping with TB and most of my knowledge are with TB than other shrimps. As such, I would like to chip in my knowledge.
TB and other soft water shrimp, such as CRS and CBS variants, absorb a lot of nutrients through water column. Since they are used to mild acidic water that has a lot of bioavailable nutrients, they are very inefficient in absorbing them when you compared them with Tiger shrimp. Hence, they will need an environment where there are enough H+ ion to reclaim the precipitated nutrients. However, having pH lower than 6 will create more problems. H+ ion will increase the oxidising effect and the shrimp will need more Calcium to combat it; cell will die easily from oxidation. Increasing the acidic of the water will tip some chemical equilibrium towards the acid side. For example, encouraging NO3 to form nitric acid that is toxic in large quantity.
As such, the optimum pH for TB or any soft water shrimp will be 6.2 to 6.6. Given said that, I tested to keep them at the extreme end of pH 5.8 and 6.8 does not shown apparently adverse effect.
If you are selecting ADA AS substrate for buffering, I will suggest you to go for Amazonia instead. Africana will be too acidic and later on, you have to put aragonite in the filter to prevent the pH from dropping that will kill shrimp. If you prefer aquasoil, you may explore other brands too. I had used Elos Terrablack and it is good too. Although not as rich as ADA AS when you are keeping plants, it is faster to setup (less leeching). There are many other brands out there, such as the Benibachi Squiggle mentioned. Just beware on those Taiwanese or Chinese brand. They usually leech a lot of acid on first week and became inert in the second week.
Alternatively, you could go for inert substrate and buffer the water with peat filter media. The benefit of this is that you will be able to control the pH consistently by the amount of peat filter media, and inert substrate does not leech much stuffs (such as organics and silica) into the water column. The cons for inert substrate is that you will need to provide the shrimp with mineral via diet and water column. I don't think it is really a bad point because even Aquasoil will deplete shrimp usable nutrients within a few months (most of the nutrients are trapped under the substrate and only can be used by rooting stem plant). Hence even with aquasoil, you will need to supplement the shrimp with nutrients sooner than you would expect.