I have to admit that I didn't really use Digicheck on Mac yet, so here are my first impressions:
CPU load:
CPU load on a 2.8 gHz C2D for "Hardware" based level-meters is around 3% when the CPU is clocked to maxed. When Speedstep clocks down the CPU to 1.6 gHz CPU load rises to around 4%.
According to the helpfile DigiCheck should only use around 1% for calculating the graphic-display. But the relatively "high" CPU load even happens when DC is minimized or hidden.
Measuring Playback/Output:
Do I understand right that DC on Mac can only measure playback/output for level meters because CoreAudio doesn't allow to chose playback/output? For me that's a big drawback compared to the Windows version, because I'm mainly using the Spectral Analyzer.
Sure you can workaround that restriction by routing the output back to an input via Totalmix, but I'm using the Fireface for live effects, which means I'm going from input -> DAW+FX -> output. So I cannot just route outputs back to inputs without major feedback problems (ouch).
Also according to the helpfile using Totalmix and DC at the same time leads to wrong level metering.
Settings Dialog:
In order to switch a button of the Settings window you first need to move the mouse-pointer away from the button. It is not possible to just switch a button on/off while the mouse-pointer hovers over the button.
The "AUTO" setting for "Top Level" on the Analyzer switches the display only upwards (towards 0 dB) but not downwards (towards -140 dB). That's a problem I had with the Windows version in the past, too.
Helpfile:
Please include a shortcut to the Table of Contents / Index that's permanently displayed at the top of the helpfile window (like seen on Apple's Preview and ITunes applications). Or maybe just turn the Index into the startpoint/homepage instead of the Overview.
Starting in "Overview" then scrolling all down to reach the Index is quite inconvinient. And after clicking through several links having to hit the back button several time or returning to Overview just to scroll all the way down again isn't perfect neither.
The help on Bit Statistics & Noise is missing btw. fryingpan
Hope my "rant" (you know me, they ain't rant, but constructive criticism) help to make this a better product.