BFD works fine with sub but not recommended for full range speakers. If you really like those M80, then try your best to play with the M80 placement regardless how many furnitures you'll have to move. If that is not possible, then your best option is either buy or build yourself a first order highpass crossover (6dB/Octave), 2nd order(12dB/Octave) is way too steep and cut off too much bass so you dont' want that. Try rolling off point at around 45~60hz(since you said your room has a spike at around 32hz and 40hz), a variable crossover network has better flexibility, do a search for Harrison Labs, their stuff are decent. If you don't feel comfortable messing around with crossover then you better off downgrading your M80 to either M60 or M22ti, they have smaller footprints, less bass, and forgiving on placement. the safest bet is M22ti.
