G5 & Logic 8

First time here, I hope someone can advise in terms that I can understand. I am running Logic 8 (version 8.0.2) on a G5 (running OS X 10.4.11). The processor is a 1.6 Ghz with a 1.5 GB DDR SDRam. All this info copied from the mac, I dont know really what it all means!
The G5 is used solely for sound recording, nothing else, (I have a small home recording studio) The problem is when I start up there are a number of sound input/output options in system preferences that I dont need, never the one that I want, which is an Alesis Multimix connected through firewire, how do I edit all these other options and make Multimix my default? Also the computer is running at its limit (or so it keeps telling me) Can I upgrade something to make it more efficient? I have to keep changing the buffer size to get a clear sound playback. The sound is often distorted, I have found that changing the buffer size (up or down, doesn't matter) will correct this.

romanytony said:

Also the computer is running at its limit (or so it keeps telling me) Can I upgrade something to make it more efficient?

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I don't have that sound hardware, so can't help there...
You need to help us understand what "running at its limit" means. How much hard drive free space do you have? (Highlight the HD, then File > Get Info)
You can upgrade RAM and hard drive.