I do not have experience on that. But nowadays is ongoing a trial with abiraterone plus enzalutamide ( but with analog LHRH) a more active antiandrogen.
I have 5 patients with abiratetone and prednisone withouth analog LHRH and with cartration levels of testosterone. I readt that flutamide could improve the results of abiraterona.
This is not a very logical approach. Rebound elevation of androgens occurs within a few days after abiraterone monotherapy due to high gonadotrophin levels, so your flutamide will be trying to block physiological or supraphysiological androgen levels before very long.