I realize that this post is 6 years old but I have recent experience testing current Mackie pres against other pres. My current setup has a ONYX board, a Focusrite ISA ONE, RNP, and a UA Solo 610. Mackie is equal to those pres and my go to pre for most recording. The RNP sounds very similiar sonically, the Focusrite is 'sheeny' and clear and the UA is thick and a bit warm. The Mackie ONYX pres fall right in the middle. They are bit low in db gain for LD dynamic mics.
At first I really didn't want to believe that my $500 ONXY board (with several pres) sounded as good (though different) than my single $1000 and $500 pres. After listening tests with multiple 'middle of the road' mics (Blue Blue Bird, SM7, Blueberry and MXL 4000) the Mackie always sounds great, always. It stacks up nice in a mix with mutliple tracks.
I really wanted to hear a genuine difference (besides color) in higher end pres but in this case Mackie happen to put genuine 'boutique' sounding pres into thier board.
Much respect and blessings,