Not to mention how much you're giving up in content, features, and track count compared to PT 8 LE that came with the Mbox family originally. There's no way I'd want to go from 8 to Express - you gain ADC and AAX compatibility but you lose like 30-something audio tracks, tons of instrument tracks, busses, and so on. This is a huge step up over PT SE that comes with some M-Audio interfaces, but it's still not something I'd be using if I was used to something more advanced (which, btw, I am personally...
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And if you don't have an iLok, you need one as PT Express system requirements requires a USB port for one, which should be included with new Mbox purchases.