Have you heard of thaumatin? It’s marketed in the UK under trade name, “Talin” and is often combined with stevia. It’s not really common in the States. That said, it’s uniquely capable of masking fishy flavors and bitterness.
The thaumatin protein is from the katemfe fruit of West Africa. I stumbled across it in my research when trying to find ways to mask the fishy flavor (or flavour, for you Talin users) of choline. I know you guys have essentially locked down the formula for version 1.0, but this might be something worth experimenting with in the future.
It’s extremely difficult to get in the US. I’ve seen it in some products but not sold on its own as a flavor modifier. The only instances I’ve seen it available on its own stateside were as fishing bait enhancers that were not food grade. So using it in DIY Soylent seems out of the question. This is actually a good thing for you, as it further differentiates the commercial product from what we can make on our own.