I personally use a Invalid Link Removed 16-channel USB interface, into a laptop running Windows 7, with Sonar X1.
The limitation is not so much the CPU power, as the interface of choice, and whether you intend on live tracking of the sound (bouncing the mixed sound back from your PC to the PA system).
With this unit, I can record all channels simultaneously at full resolution... but with a significant caveat. I need to configure my PC to absolutely not interfere with the USB bus or the hard drive writing speed. If I do not, the recording will be interrupted.
What does this mean? Configure your PC to turn off ALL un-needed services (yes, temporarily disable Windows Update, your virus scanner, defragment before you start then disable the service, disable your wireless and network cards, etc.). Turn off Aero, and in fact turn off all UI enhancements. Etc. With this config, I regularly record 8 microphones and 3 line-level devices, and obtain 11 uninterrupted 4-hour long tracks of our jam sessions for later slicing and massaging. (I turn everything back on after a reboot).
This unit cost under $400 used. YMMV
But ultimately, the 2442FX is an analog mixer... and there lies the problem, since your stated requirements are to be able to record separate digital channels.
Ah well.
Dekker