Shrimp breeders would love to have your water parameters. Having said that, if you are injecting CO2 to reach optimal levels, I would worry about pH crashing. Many, if not most people use this substrate for their high tech tanks, along with r/o water. I guess they are raising their KH somehow, whether it be calcium carbonate additions, rocks or baking soda. I personally don't use this substrate in my high tech tank because of this reason. That, and I don't see really see the need to feed plants via the substate when dosing ferts to the water column anyways. I did use Fluval Stratum on my latest low-tech scape (for aesthetic reasons) and I'm facing similar issues. I have somewhat soft water (dKH=2 and dGH=3) and the FSS buffers it down to 0-1 dKH. I'm doing the same as you by just adding baking soda. My KH isn't dropping as quickly and believe I'll be able to exhaust it's buffering ability before the the cycling finishes. I don't think I'll need to take any extreme measures to bring it up.
Any form of calcium carbonate (aragonite, crushed coral, oyster shell flour, eggs shells, etc.) in a stocking or mesh bag tucked in your filter somewhere would be a way to slowly raise the KH for long term.
I'm curious what others have to say on the matter, being as aquasoil is the holy grail of substrates for planted tanks and used by so many folks here.