Hi. I don't think you need the individual outs at all. The optional Mackie Firewire interface converts everything from analog to digital INSIDE the board and sends everything to your computer and each channel is recorded SEPARATELY as wav files with their free software that comes with the Firewire Interface. 8 Channels==one cable.
I have the 12 channel Mackie Onyx board and the preamps are fantastic. For the money, I don't think you'll get the same audio quality with anything else.
Also, I think you can get by with the 12 channel version. The first 2 channels are XLR with a switch that activates a built in direct box if you need it. The next two are straight XLR inputs. The last 4 are 1/4" stereo.
Mackie Firewire Interface Info:
http://www.mackie.com/products/onyxfirewire/ Here is part of Mackie's description of the Firewire interface capabilities:
"The Onyx FireWire Card is a true first. This user-installable 24-bit/96kHz card transforms the Onyx 1220, 1620 and 1640 mixers into fantastic-sounding digital audio interfaces capable of sending up to 18 channels of audio to your Mac or PC — without the need for additional converter boxes or hardware. Thanks to the use of flagship Onyx mic preamps, superior analog circuitry, and class-leading A/D converters, Onyx mixers with FireWire rival the sound quality of dedicated audio interfaces costing many times more. Not to mention the simplicity of plugging in up to 16 microphones and sending them directly from the mixer to your computer... and monitoring a stereo mix back through the mixer."