Initial Testing of the BK MONOLITH I had no problem unpacking the weighty Monolith on my own as I actually followed the instruction leaflet supplied by BK. Build quality is extremely good and looks like a £800 sub in the cherry veneer with the corner fillets particularly attractive. I was very happy to see an optional XLR balanced input. Dont see this on many subs. I set the frequency control to LFE and the volume to 11 0clock with all other settings remaining the same as for the XLS200. On music the first impression was one of effortless ease. This sub goes LOW. I used the CD Between the Sheets by 411 (pronounced four-one-one as corrected, courtesy of my Granddaughter) which I use on all my subs and know the bass lines extremely well. The sub followed relatively fast tracks with ease. The title track bass sounded like a sledge hammer causing vibrations in my listening chair. I also scanned down the SKY music channels finally ending up on Classic FM my favourite. On classical music the refined nature of the Monolith really became noticeable as did the seamless integration with the main JBL control monitors. Bit of luck with the settings here I think. Fatigue after four hours of listening? No none at all. The unit was tested on the carpet no spikes or vibrapods, as yet, but no ornament rattling was heard. Compared against the XLS200? Unfortunately I have sold my XLS200 to make way for the big boy so cannot carry out AB testing for direct comparison. However it is not easy as the XLS200 is an excellent sub and good on music. In my very limited four hours of music listening on the Monolith the depth was there plus a certain excitement. Can I put it this way I liked the music on the XLS200 but love the tonal sound of this giant, but other ears may disagree. It was effortless in giving the impression of vast amounts of power in reserve, it just sails along, and has deeper bass at lower volume. Basically it is what you might expect from a larger driver and a much bigger box.(Sorry, veneered enclosure) It was very easy to forget at times that the sub was indeed active. Personally I particularly like this characteristic. Further comparisons in due course as I have yet to test on AV. Now that will be an experience. Also electronic testing for those of us who are interested in such things but . WARNING! May contain technical language. I hope the above helps those considering a Monolith but it is my opinion and musical tastes are personal and vary greatly.