Well the fact is that OS X does not use a Microkernel and never did. It was a lie. To keep the Apple reality distortion bubble from popping people have created the concept of 'hybrid microkernel' to describe the OS X kernel as if that was some sort of CS concept.
Which all that it means is that Apple copied the NT kernel design approach by incorporating some features of microkernels into what ends up being fundamentally a monolithic design.
But as far as audio stuff goes I am told that Apple's CoreAudio is actually a compelling feature over what is available in other operating systems. It's designed with music production in mind.
To get the best out of Linux it is still very tedious and highly technical.
* Installing and configuring Jack
* Configuring your applications to use Jack
* Purchasing a audio card with good performance characteristics. (Intel-HDA, while it is fine for music playback, is not designed for low-latency performance regardless of what drivers you use on it)
* Installing a custom OS kernel with *-rt patches.
And a great deal of learning the ins and outs of how to manage all the above.
Generally the biggest difference between the the actual workflows of Linux vs Windows is that instead of using big music production apps with plugins you use a lot of smaller applications chained together through Jack.
Now keep in mind that it has been a _long_ time since I mucked around with this stuff.
But I have a simple piano-style M-audio midi controller. It connects to the PC using a USB connection.
So the workflow went like this:
USB Controller -(jack midi routing)-> Software Synth (I forget which) -(pcm audio routing)-> Alsa Modular Synth (for effects processing) -(pcm audio routing)-> volume controls -(pcm audio routing)-> digital out on my sound card --> digital receiver --> speakers.
All in all I got the system to reliably operate to the point were I could not notice a delay from when I press a key to when I heard the sound.
Of course this required a couple hours of mucking around and setup. Debian by default could barely do software synth on it's own before I started customising it.
The situation has improved somewhat with the introduction of custom Linux variants in the form of 64Studio and Ubuntu Studio and things of that nature. So at least the software setup is mostly taken care of.