Where to start...
I would advise you to buy an Airport express and plug it on the back of the BS9000... That way you can transmit the music wirelessly. The transmission uses the lossless algorythm so it does not loose any quality and the Airport express has a Digital out.
I did not know the BS9000 had a digital in...
Now, I think someone has told you a lot of rubbish here... It is incredible what people can say...
ITunes will recognised all your MP3 or AIFF, iTunes on a mac will not recognise WMA.
With you current PC, I would advise you to install iTunes, and import everything in the library, and you'll see by yourself.
iTunes for PC does recognise WMA (without DRM) and is able to import them, but it converts them. If you use something different from Apple Lossless, you'll lose quality. If you use lossless, you'll have the same quality as the original WMAs.
Apple lossless are not compatible with other platform, that is true, but because it is lossless you can later on use iTunes to reconvert them to AIFF, and use another tool to convert them back to whatever you want. The conversion to Apple Lossless to AIFF is... well... lossless... The conversion to another format will only loose quality if you use a non lossless format.
Compressed files you bought from the store are in 2 different formats... some songs are with DRM some other songs are without DRM (iTunes+).
The songs without DRM are in AAC format, becoming widely used, on mobile phones and other digital media player, so not a big issue there.
For DRM protected songs, you are allowed to burn a CD with them, and use that CD however you want. If you reimport that CD in any platform using a lossless format, you'll keep the same quality as the file you've bought.
As you do not need a mac to play with iTunes, download it for free, import your songs and see if you're happy with it.
The good thing is when you have your mac you can copy you iTunes library from the PC to the Mac, and you'll keep all the organisation you've done.
Enjoy your mac, and by the way there is, only TODAY in europe, good discounts available if you order online.
p.