[Obsidian Dragon]

Your system is quite old and technology has moved forward far beyond those times. Perhaps the best way to solve the performance issues would be a new computer and interface. If you are comfortable with computers and hardware, going with a Windows on an Intel i7 or i9 is more cost effective. If you prefer to have an easier setup that has less variables, an Intel-based Apple Mac might be a better option. The M1-based Mac's are not officially supported yet.

As for the interface, any modern interface should work fine. For a single input (or just a few at the same time) USB3 interfaces are fine. If you need a lot of inputs and outputs at the same time (8 in/8 out or more), then Thunderbolt may make sense

These are just general ideas and not specific recommendations for any particular brand or model.