Go for sub or larger speakers?

I just upgraded to REL B3, and I can't believe how well it integrates with Harbeth C7ES3s.

A lot depends on room size, I think it is easier to get a speaker/sub combination to work in a smaller room. But in the end it is a question of personal taste. I believe most of the integration problems arise from crossing too high or playing the subs too loud or a combination of the two. I haven't had much trouble integrating mine.

Thanks for info, one more question, would I need to employ filters on both main speakers (highpass) and sub (lowpass) for proper integration, or I can leave mains as they are and only filter higher frequencies on sub?
My speakers are 6dB down at 40Hz, I was thinking of connecting subs to 2nd output on pre-amp and employ filter on sub only, in order to avoid additional signal processing for main speakers.