It is these chemical above that are increasing TDS. Anytime you add chemicals/minerals, it increases TDS.
Preferably try to obtain a GH+ (not GH/KH+) remineralise for RO water, don't rely on Buffer and Regulator. This option has the extra benefit of no additional phosphates (Discus buffer and Regulator is a phosphate based buffer).
EG, https://www.bossaquaria.com.au/shrimp-king-bee-salt-gh/
https://aqualabs.com.au/products/saltyshrimp-bee-shrimp-gh-110g
https://nanotanksaustralia.com.au/product/shrimp-king-bee-salt-gh/
If you prefer, use the Discus buffer but leave out the Regulator.
Amazonia + RO water should in theory give you very low pH levels by itself. Do you have any rocks in the tank? Rocks increase KH, pH and TDS.
I assume you have tried Amazonia+RO water by itself without the added chemicals and have not been able to reduce pH. Is that right?
A tank will naturally gravitate towards Acidic, as beneficial bacteria breaks down ammonia, where a buffering agent (like rocks or shells or calcium carbonates) are present in low amounts. Is your tank mature and cycled?
If you can provide answers to the questions above, we should be able to help you figure something out.