Another option you have is to write your own broker plugin that connects to your FIX-based broker. RightEdge makes this possible with its open plugin architecture. We are a customer just like you, and we have been able to write our own broker and data plugins for RightEdge.
But just to clarify... FIX isn't the lowest latency broker/data connection out there. It's a variable-field-length text-based protocol, which means an un-optimized FIX engine may have more latency than you expect. How much more? Probably on the order of 50 microseconds. So in the vast majority of use cases, that extra latency probably won't affect your trading. It only really matters for high-volume low-latency strategies that you probably wouldn't implement in RightEdge anyway.
That being said, if you're a professional trader, either solo or with a firm to back you, and if you have some programming skills or can hire someone who does, connecting RightEdge to a broker via FIX is a totally reasonable thing to do and would open you up to a wide world of brokers and trading venues.