On Win I found a free app "Always On Top", in the Cubase Vst Window you un-check "Always On Top(my as#)" top right menu. Run the "Always On Top" app set the HotKey, click the Cubase VST window and hit the HotKey.
So you could look for something like that for the Mac.

For these 2 solutions you just load the VST then load the Biab VST inside them, this way the Plugin stays on top if there is a flash message or you click on the desktop.
Use MiniHost
Direct Download Links

The other way is using PluginFlipFlop if you already have JBridgeM

ReaTrak Biab & Plugin in Reaper
Free Biab Chord Picker Tool