Regarding USB, something be aware of. If you're using a powered hub...
Power you gear, not your hub. This way you KNOW that your gear is getting EXACTLY what it needs.
The onboard sound card then? So the fix may in fact be an external audio device, rather than an external drive.
The simplest solution is to buy the sound card first. See how it works. Then buy an external drive or other gear as needed. There's not need to call Apple. You already know you want an external sound card.