LOL, Donny... I use a 2001 Mac Quicksilver for my sequencing and audio needs (although I am strongly considering finally moving to OSX and my iMac 27"). All my hardware uses PCI slots (the original ones!) and no adapter has been made to use them with PCIe or PCI-x. So my UAD and MOTU stuff has to be used with this relic..!
Mind you, well over 48 tracks of 24/48 audio is easily doable with full effects and MIDI. If you need more than this, you are overdoing it! Beatles made do with four tracks... (on much of their stuff)
I think the reason that despite the cost, I always recommend Mac's to musicians is that many of them don't WANT to be geeks. Most of them simply want the computer as the tool for music production. Having to deal with anything else is not why they want one. My experience with Mac's has always been trouble free (other than the usual HD issues, which anyone gets no matter what platform you are on if you push your HD's hard like full audio production does). I have had the time to concentrate on the software alone, and that piece of mind and lack of worry is worth quite a lot of money in the long run.
I don't want a computer. I want a DAW. I want a video editor. I want some VSTi's. Mac's make the computer almost invisible. You simply use the software. Brilliant!