Aggregate Device or CPU?

[Pull Hair Out Studio]

Hi, just registered.

Used Logic Platinum for years on PC. Decided to switch to Imac Intel core duo 2.33, 2Gb Ram, and Logic Pro 7.

I have two Interfaces running on Aggregate device (Focusrite Saphire & Mackie Onyx 1620) via Firewire direct to Imac. I mainly use the FS for recording me (2-3 tracks audio - Vocals with Acoustic Guitar and Midi guide tracks) and for outputs to headphones & monitors. Basically the mother interface! The Mackie is used for extra inputs for drum kits, live room band etc + general rigging of external devices + it will be handy to do live recordings when i get the Pro Book! During my first session on the new gear, using 2 tracks at same time, a window came up saying 'Disk too slow', and it crashed. I have recorded many tracks on the old Logic on PC and never crashed!

Is this a CPU problem or is it something to do with aggregate device??? Should I get an external processor? Should I get a different interface? Should I use only 1 interface? I have a band coming in next week with drums, if it crashes recording acoustic guitar, what will it do with a drum kit?!

Have phoned Apple but it takes ages to go through to the right person. When I get to the person, he usually has a unfamiliar accent and is hard to understand. No offence. + and + and + and ..... I have configured the aggregate device to use the FS as all outputs, when I was using Wave Burner the other day, the outputs came out through my Mackie!??? There were no configurations telling it to do so??? Help! [/b]