I'm thinking that using Microsoft Virtual PC for the MAC platform MIGHT help you there. It is software that allows you to run Windows inside a window on your MAC. You might be able to install Sonic Stage and manage music on the MD unit with it.
I don't know what you should exepct for playback capabilities for Virtual PC though. Usually virtual machines suck or just don't work for playing music. I know that is the case for another product for PCs (VMware) that lets us run another operating system in Windows or Linux.
My wife has a Mac running OSX, but the thought never occurred to me that I might want to manage MDs on it. I have a pretty decked out PC, so I never thought about it much.
Anyway, you might want to investigate the use of Virtual PC for MAC.
I took the liberty of checking the Compusa website from my area (can't think of another place here that sells MACs). It even looks like they will give you the option to buy it with Windows XP Pro preinstalled, so that you dont have to install it on Virtual PC. Either that, or you can buy the standalone one and install Windows XP or whatever you want to try on it, which is cheaper if you already have an XP license.
Here are some prices I found:
Virtual PC for Mac 6.1 with Windows XP Professional (Mac)
Product Number:305534
Brand: Microsoft $249.99
Virtual PC 2004 (PC)
Product Number:50342949
Brand: Microsoft $120.54
I hope that is something that might work for you. I don't see why you couldn't use Sonic Stage on it and manage the MD recorder over USB with it since Virtual PC supports USB connectivity.
-Ice-