In general, ML isn't in the same league as the Parasound Halo as ML is superior to the Parasound, but IMO the Halo A21 is still a great sounding amp especially considering its asking price points. I can't say that the ML23 is superior sounding than the Halo A21 as I haven't heard the ML23 so can't comment. The current new ML gears are very expensive and aren't really affordable to some people whereas the Parasound gears are much more affordable to most and Parasound Halo line makes quite spectacular gears especially for the money.
But in general I wouldn't put Parasound in the same league as ML, especially when it comes to linestage preamps.