Audacity is not multichannel recording software, as far as I can remember.
You can find some soft for Linux, do some search, but I am not sure if you want to get into installing Linux on your system.
You have missed oportunity to get free copy of Tracktion recording software recently. It was part of the promo for release of v2 of software. It is not exactly free, but it is really cheap for what it does, if you can find v1 somewhere.
Also if you like Acid, I guess you should know that there is Acid Express, but I a not sure if it allows audio recording as a full version of Acid.
If I was you I would shell some money and buy Tracktion it is great software for the money, and you can find a lot of free VST plugins on web, that will work with it.
You can also check cheapest version of Cubase, SE, and Magix Music Maker program.