Logic 8 Lacking I/O Options in Preferences, Need to Change Settings for USB Mic and Controller

I travel for work and wanted a portable recording system to take on the road with me, so I purchased 1) the Arturia 25 Analog Experience and 2) the Blue Yeti microphone. Both are USB devices. I use a MacBook Pro OSX V 10.5.8 with Logic Express 8. When I plug in the Arturia and create a software instrument track for it, the sound of whatever instrument I've programmed it to be comes through my headphones just fine. However, when I plug in the Yeti, Logic asks me if I want to use the mic as my interface. If I select yes, sound from the Arturia no longer comes through the headphones, though I can see that it is still inputting just fine. Also, sound does not come from the Yeti, either, unless I plug the headphones directly into the microphone itself. To troubleshoot this problem, I changed the main audio input on my Mac from internal mic to the Yeti. This enabled me to go back to using my built-in input/output while hearing both USB devices through the headphones while plugged into the Mac. Unfortunately, I can barely hear sound coming through the microphone and Logic is showing minimal input, as well.

Blue's website said to add the Yeti to "aggregate" in my Mac's Audio MIDI settings, which I did, and then change the audio in Logic from default to aggregate. Those instructions were for Logic 7, however, and I can't seem to find "default/aggregate" anywhere in my audio settings or preferences. In Logic, I opened the Preferences and selected Audio. Instead of offering Input and Output options, it merely has "Devices," which seems odd.

My main objective is to hear both the Yeti and the Arturia through my headphones simultaneously, at both devices' full capabilities. In the interest of space and weight, I wanted to eliminate the need for my M-Audio ProFire 610 while on the road. I'm wondering if there's something I need to select within Logic in order to have I/O options offered to me...or if this is all a conspiracy to get me to upgrade to Logic 9!

Any assistance offered is greatly appreciated! I just want to make music as smoothly and efficiently as possible while away from home. Thank you!

~Britt~