Promix bx already has a Mycorrhizae ...
Pro-Mix[SUP]®[/SUP] BX Mycorrhizae[SUP]®[/SUP] is a general purpose peat-based growing medium containing, a beneficial mycorrhizal inoculum (Glomus intraradices). These microscopic fungi attach to and colonize the root systems working in symbiosis with plants. It benefits plants by increasing water and nutrients acquisition (especially Phosphorus, Copper and Zinc). This symbiotic relationship between fungi and plant, results in an overall improved plant growth.
So try to find a micro nute that's suited for the nutes you use.
The balance is important. I use micro brew, but only after the soil has been flushed, and only use 1/2 doses even though it's part of the fox farm line.