Parallels generally seems to do better when it comes to 3D acceleration, but as nevcariel says, I don't think you will have much success using madVR inside a VM.
I would probably avoid any hardware that relies on Firewire - it's pretty much a dead interface these days now that even Apple have dropped it from their machines.
It may one day get video support with a basic renderer, but nothing advanced like madVR, unless some 3rd party has something in store that can be reused (like madVR on Windows).
My guess would be that Media Center will use CoreVideo if they add video playback to the Mac version.
Programs like Media Center and things like LAV Filters and madVR are one of the reasons I'm using Windows these days.
The main applications that I relied on, on my Macs were actually multiplatform (Photoshop, Lightroom etc.) so there was little actually tying me down to that OS, other than preferring the workflow I had there.
But OS X has been gradually moving away from "pros" ever since 10.5 and has been "simplifying" the OS ever since, in ways which breaks a lot of how I liked to work in the OS. (Mission Control is a poor substitute for the old Exposé and Spaces, Fullscreen apps kill off multitasking etc.)
10.9 looks to add a few more "pro" focused features back (and for the first time, useful multi-monitor support!) but I haven't found anything lacking about my Windows setup these days. It's been pretty solid since Windows 7, and Windows 8 is even better.