Firewire and multi-channel devices generally are often designed primarily to work with ASIO driver. It seems that Windows drivers are often added on as something of an afterthought. Unfortunately Audacity can not be distributed with ASIO support due to licensing restrictions (though if you build Audacity from the source code it is possible to compile it with ASIO support and it is legal to do so for personal use. Unfortunately this option is rather too “programmy” for most users.
Being stuck with often not very good Windows drivers, many users have reported difficulty getting their firewire/multi-channel hardware to work with Audacity. A simple option that some users have taken is to use an ASIO program for doing the recording and then use Audacity for editing.
On the other hand some users have reported that Audacity works fine with their firewire/multi-channel audio device.
Although we try to encourage people to give feedback about their hardware, there are only a few snippets of information on the forum. (for example here: Sound Card Reviews )
Me too 
Firewire still is big. USB2 does not overcome the problem of CPU dependency.
It’s not just about speed, USB is designed for burst data not sustained data. Sure you can buffer the data to cope with gaps between the bursts, but that introduces latency which makes it useless for many DAW applications.
USB 3 has a major advantage over USB 2 for audio applications in that it supports full duplex, but it is still to be seen if it can live up to the hype in real world applications. Firewire is a well established standard for professional audio and video work (though high end equipment tend to use custom interfaces in preference to USB or Firewire). It will take more than hype to make Firewire obsolete.