Surround sound recommendations!!

Hi, i am new to the forum, at the moment i have a koda 2.1 system too which i have added 4 more speakers so its now a 6.1.

I have had it for a few years now and want something with HUGE, undistored bass. Mine is quite good but when abouve 80% volume the bass is at a good level but distorts. 

i was wondering if i could have any recomendations of surround sound systems with big bass which sound good.

my price is avout £400 ONO

thx