Reverting back to the OP's original question, The room dimensions are quite large, 6m x 5m with a 6m void ceiling. and his inquiry about obtaining a sub to suit the room and his bass requirements. Really 6 x 5 is not a large space , and nothing that a large pair of floorstander speakers can't handle and provide all the volume required. Unless of cause your a mindless doof doof addict. But having said that, small bookshelves simply won't cut the mustard, and apart from the fact they won't produce any bass, then and only then is a sub required. Really my advise would be to beg, borrow, or loan a pair of suitable sized floorstanders together with decent amplification [ forget the AVR most if not all is simply rubbish ] and you might be surprised to hear everything you need. While not wishing to self promote myself my main room 7 x 6 contains two stereo systems and a basic H/T. Nothing warrants a subwoofer as all my floorstands with mono-bloc amplification, cover the full sound spectrum Nice work of completely missing on OP's room height. I know that basic math is hard for some folks, so I've already converted these strange metric units into normal ones, and his room volume is over 6 thousand cubic feet. AH page right here says that over 5k cu ft, for room size, is considered an extreme-sided room. https://www.audioholics.com/loudspeaker-design/subwoofer-room-size
