I have heard both back to back at a dealer demo. The 3.6 was on a Mcintosh 252 and the 20.1 was on Mcintosh 1000 watt mono blocks.
The 20.1 have a LOT more bass. They dig deep and have good output. The midrange is not as forward on the 20.1 and a little more laid back. The highs sounded the same to me. I actually really like the forwardness of the 3.6 midrange, it makes vocals standout.
The 20.1 are a big up grade in sound quality. But $13,000 is a lot to spend on Magnepans with their sub-pare build quality...
The 20.1 have a LOT more bass. They dig deep and have good output. The midrange is not as forward on the 20.1 and a little more laid back. The highs sounded the same to me. I actually really like the forwardness of the 3.6 midrange, it makes vocals standout.
The 20.1 are a big up grade in sound quality. But $13,000 is a lot to spend on Magnepans with their sub-pare build quality...