Just curious which indirect toning technique you plan on using. Unless you use very special dyes you shouldn't have an issue with acid, and if you thoroughly tone with Sulfide neither acid nor ferricyanide should be a problem. I suspect you want to red or blue tone, and some of the resulting compounds will be attacked by ferricyanide. If that is indeed the case, you should be able to work with Ammonium Ferric EDTA based BLIX regardless of pH.