Subwoofer for lab8000

I'm wondering if any one has any advice I have an old friend who has a pair of lab 8000 connected to active kit wants to add a subwoofer non bang and olufsen one. The problem is he has a budget of £400 are there any good ones at that price, any recommendations would be appreciated

Hi not sure which ones are compatible, but I would definitely think about the size of the room and where the speakers are - I added a BL2 to the same setup and it made a huge difference but because the room was small you could hear the bass coming from the left, so it and the speakers are now in a much larger room, replaced with Beovox Pentas in the smaller room - which sound great!