I have ML 2s12s 20s 40 and 60xts as well as a bunch of other brands.
the 60xs require a beefy amp that can handle 2 ohm loads. the fancy smanshy yamaha top of the line reciever cant power them to satisfaction and lesser ones are not even worth listening to.
last night I went to a friends with 7 pairs of speakers set everything up and proved high end recievers are worthless unless it is a sunfire or similiar.
at an ultra high level I could yell and not be heard and the 60xt/sunfire was so clean you couldnt tell it was so loud until I started yelling and suddenly turned the sound down. we only tested recievers no seperate amp combos. the lesser MLs were not able to repeat the yell test. they were clean to a point but my friend could still hear me and did not have the depth or dynamic range the 60xts had.
a skeptic became a believer and after we used his reciever(s) a few times it was shut off and sat in the corner for the rest of the night. I left him with the 20s and a smaller sub until he can buy a pair for himself. he just bought a 9k snowbike and has to wait a bit.
M