The LX20 is the low end of the ADAT food chain and the M20 would be at the top of the chain. While I know the M20 has better converters, I'd bet you'd be hard pressed to hear the difference between the two. Now the LX20 is equiped only with RCAs forf the analog outputs (unbalanced, -10) where the M20 will have the capability of balanced, +4 outputs. This can have a big impact depending what you're driving it with and what you monitor with.