Sound Card vs Interface

Question

Im currently using a MIDI/audio interface to connect my keyboard, laptop and speakers. I use the sounds from my keyboard with Logic, as well as using it as a controller keyboard. But Im upgrading to a desktop and was wondering if its worth getting a decent sound card or sticking with an interface. What are the pros/cons? I assume there are enough I/Os on the Mac Pro to facilitate this set up? Can you chose a sound card to put in the iMac?
Also, my current interface is 44.1khz, but my keyboard runs at 48khz. Is it a must to have an interface/sound card also at 48khz.

Answer 1

Finally!  I wrote a reply a few hours back but the fine folks at Adobe took the site down just before I hit send!  Lucky I saved it elsewhere because the "recovered post" was only the first couple of paragraphs.
Anyhow, take 2.
Well, first off, your Mackie Onyx mixer has a firewire interface built in so it, in effect, becomes your sound card.  The one in your computer isn't involved in the recording/playback process at all (at least not unless you're trying to do something like monitor via the computer card rather than the mixer).  Therefore, buying another sound card/interface won't help at all.
Similarly, audio dropouts aren't a latency issue, at least not directly.  Latency is the delay in the audio as it does the round trip via you sound interface (mixer) and computer.  It's more of an issue for musicians trying to be beat accurate as they over dub tracks.  However, the latency controls could be affecting your drop out problem.  The latency control in Audition is effectively controlling the buffer size--and having a larger buffer (which increases latency) also gives you playback more protection against glitches when your computer gets busy doing something else.  So...the first thing to try is increasing the latency/buffer size on the Edit/Preferences/Audio Hardware menu.
Another thing to check is that you're using the latest drivers from Mackie--check their site and download/install the latest if there are some available.  If there's a choice, go for ASIO drivers rather than MME if there are some available.
Also, I mentioned your computer getting busy with other things--for serious sound work shut down everything else on your computer.  Pay special attention to networking, wifi, and anti virus software, all of which are usualy prioritised to grab processor cycles over your sound work.  Also make sure you shut down all system sounds.
Hope at least one of these suggestions works for you.