Best Crossover frequency for Sub

[BlueThunder]

Hi All,

I have my surround sound system set-up and running this week.

Receiver - Pioneer VSX LX70
Speakers - Monitor Audio (RS6, RSLCR, RSFX, RSW-12)
http://www.monitoraudio.co.uk/range.php?range=2


I am wondering what crossover frequency to use for the Sub. Most advice and THX seems to recommend 80Hz. This is for movies 5.1 and stereo tracks expanded to the rears)

When it is set to this the front L/R speakers to 80Hz they seem to be under worked. The front R/L are tower speakers and have a tweeter, mid range and bass speaker.

When I set it to 50Hz the front L/R seem to delivery a more balanced sound and appear to be comfortable in doing it, but also the surrounds are now working a lot harder (2 tweeters and 1 bass/mid range)

What to you thing the best setting is. If it is 80Hz do you think that the large front L/R are an overkill and I should have went for the smaller option .

Really appreciate you help on this. I will try to add a picture of my set-up later today.