Logic Pro 8 Easy DIY: Build Mega Audio Interface from Multiple Interfaces

Some of you probably already know this. I did. But I forgot about it. This is pulled from FrontPanel, Emusician (magazine), 06.08:

Build a Mondo Audio Interface-for Free

Got an extra computer audio interface lying around? If you're running Mac OS X 10.4 or later, you can aggregate the interface with other audio devices (USB, FireWire, PCI, or built-in) into one giant combination interface. I've used this trick to run two USB mics at once. I also created a quadraphonic speaker system by aggregating a Zoom H2 recorder (in USB interface mode) with my Mac's built-in audio output and making the H2 the master clock. That let me hear the Hs2's 4-channel recordings in glorious surround.

To aggregate audio devices, plug them all in and open Audio MIDI Setup [in the Applications > Utilities folder of your start up disk]. Select Open Aggregate Device Editor from the Audio menu. Click on "+" to create a new device, and check off the I/O you want. [...]​
We should talk. I'm having an issue with my Hammerfalls not passing audio through to my speakers. I can see the meters in Logic, but it won't pass the sound to the output. Do I need to suck it up and tick the Software Monitor box? I have one Digiface and two Multifaces hooked up.
I'll call you today. Sorry to hear you are having trouble, bro. Software Monitor box won't help with that. It's only used to hear input signal during recording (albeit with the much dreaded buffer delay betwixt).
I figured there was a way around using the software switch. It has been some time since I've used the hardware options. I've been so committed to using the tools I have with me, I haven't even wired a single keyboard up to my speakers. Now, I'm putting my stuff back together and I've forgotten so much about how I did it before. Five years is a long time. The OS has changed, and my machine is different. I'm not even using the UAD or PowerCore!
I don't currently have any audio devices attached to my computer, and the menu item is dimmed.... I'm assuming that it will un-dim once i've got the interfaces attached?
I'm now focusing on MIDI so I can sequence. I just ordered a Remote SL 25 with a bag for my portable solution. I need to get a solid hub solution for controllers and get my audio back up and running. I may be forced to cascade via SPDIF until I get a proper solution running.