You have moved the P3 closer to the wall behind them? That can help with bass, of course.
I agree with @dekay that different subs would blend differently with the P3. I am using a small B&W with good results. Last time I looked a measurements for a REL, it rolled off quickly at higher frequencies, which would be great for many applications but maybe not ideal for yours. This is nothing against REL, just a potential case of horses for courses.

