Which is good quality (low level) high/low pass filter?

[dlaloum]

Yes, it's where the low pass filter slope and high pass filter slope "cross" "over"

Yep, and obviously you choose both filter slopes and and frequencies to achieve whatever goal you have in mind - there is no "one size fits all"

Although in our current age of digital EQ AVR's with Dirac/Audyssey etc... one can opt for a "looser" specification and then compensate - but the closer to the mark the XO is, and the less EQ has to do, the better the result is likey to be!