Well, it seems that I have to admit to failure To Get Both Internal And External Speakers To Work At The Same Time on my 24" iMac.
I purchased a cheaper Philips 2.1 speaker system to enhance the sound of my iMac but I wanted to also have both the external speaker 2.1 setup (3.5mm stereo plug only) and the iMac's internal working at the same time, as they actually produce a decent sound. But not to be it seems.
Unless of course some has found a simple way to do so.
It seems Apple's more recent OS X Macs can't even do what was possible on my old Macs with System 7.x and 8.x + versions. No "bridging" allowed it seems that used to be available with the old OS Systems and old Macs.
I Googled and tried all kinds of stuff, including using my Griffin USB iMic and as I posted to our local VMUG, close but not close enough.
And unfortunately, the default SL OS X Sound pref only allows the user to choose between the iMac's built-in output source OR the headphone port for any external connected speakers, but not both for some strange reason to me.
But wait says my old Mac brain when it clicks in, I have an old iMic USB device I could use to plug in the external speakers into and then use my "Audio MIDI Setup" (Utilities) to set it up using the "aggregate device" to configure it and the internal speakers.
But no success showing until I gave up and restarted my iMac.
I was then presented with the "Sound" pref pane window with an "Aggregate Device" option showing.
Ah finally, but success was soon to disappear when I clicked to select the new option to use and was met with the message:
"Settings for the selected device: The selected device has no output controls."
Bummer, so close but yet so far….
And I had to select to use either one or the other internal or USB iMic options for most normal speaker output.
Oddly with the "Aggregate Device" selected, all OS user sounds (alerts etc.) are not available or sound, yet iTunes and other stuff will play all audio - but only via the currently connected external speakers connected to the iMic.
There has just got to be some way to get ALL connected speakers working somehow, but I'm just about to give up trying!!
So I've basically given up unless someone can show me a way to actually get such a setup working and I really don't understand why it should be so hard to do.
Gheese Apple!!! This iMac is what you proudly describe as a "multimedia Mac", yet it can only output audio to a single audio device at a time?? How bizarre is that.
And yes I did search the forums here, but the high-end audio systems some members are using is waaay overkill for my want's or needs.