I would choose the Mackie if I thought I wanted to record a band all at once or use it as a mixer for a gig. IMHO the preamps on the Onyx are superior to the focusrite at that pricepoint.

The 1640i also allows you to route 16 tracks back so you can mix with real faders, eq and external processors via the inserts and aux send/returns.

Just got mine last week. Ive used the older 1640 for 3 years and decided the added features on the 1640i were to great to pass up.

Plus in a studio setting, the 6 aux channels can feed 6 individual headphone mixes to your musicians (along with a headphone amp that supports 6 channels)