I have a number of solutions for you based on some experience I have with TradeStation.
If your code is written in EasyLanguage, you should try and trade with TradeStation directly.
We are an IB to TS, and would be more than happy to facilitate you.
We charge the same commissions without any added markup.
However, I also would like to share with you some other solutions that may be viable.
A program we used to bridge to TradeStation is called InsideEdge that has a great programmer behind it (Peter Nannis). I suggest to connect it to Rithmic while TS sends it it's signals. AMP who we clear through as well offers it with low margins. We have used this solution for many years when we ran in-house automated solutions. It was rock solid stable and had low latency execution while both machines were on the same terminal.
I think that InsideEdge is one of the less appreciated software out there while it has good DOM , ,stable execution capabilities and feature rich charting.
Lastly, you have the ability to connect TS to OEC Trader which connects to TS and at the same time also has the ability to allocate trades within the software to the appropriate accounts. We made a video about it
I know I "dumped" here tons of data, but I hope you can make the right decision appropriate for you.