As noted by 'liveaudio', the Echo Layla 24 works well in a rack-mounted older (2002?) desktop P4 machine (512 mb RAM, speed unknown).
For a long while, we had one Layla and it performed great with 8 tracks recording simultaneously.
Now we're using two Laylas to record 16 tracks at once. (Too lazy to re-route!)
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I installed a faster and larger hard drive just for added measure, but it worked well with the original HD.
As a sidenote, you must have the two cards synchronized, and the respective outputs mapped correctly in AA, which was very easy to do.