Quote from speculatus:
I was trying to avoid broker APIs at any cost.
In my ATS I have implemented the position manager, use third party market data provider (through an abstract interface), and FIX for order routing, so it's completely broker independent.
This way the only thing you need is simple FIX certification and configuration changes when you switch between brokers.
I believe this is the only way possible on the long run. When you need something done right, you have to do it yourself.
I believe your position manager is to get you information on your account balances, positions, order status etc. How did you implement this? through FIX or broker-dependent API?