Mac does support aggregated devices, that is no guarantee this combo will work.

As for PF 2.5 with Profire, the PF license you have is tied to your UX, so you can not use the Profire with PF standalone, you can record with the Profire and add the PF plug-in post processing using the UX as a dongle. Line6 does sell a separate hardware independent PF 2.5 license the will work with other USB ASIO devices, so I 'm not sure if it is compatible with firewire. However, if you get to the point, you can purchase the license and get your money back within 30 days if it doesn't work out. If you go that route make sure to purchase the hardware independent version, NOT the iLok, there are NO refunds on the iLok purchase.