The card or device would depend on your workflow. If you will be capturing from tape vs. transferring from P2 or other storage card format. I’d recommend any AJA product https://aja.com/, but there are good choices from Blackmagic Design, too https://www.blackmagic-design.com/ .
After you have your card/outboard device you could attach your Genelecs directly to the card output, although, I’d NOT recommend doing that. You wouldn’t have good control of the monitors that way and could easily overload them. You should have a mixer that will accept inputs from any machine, mics, etc. The output of your card would go to inputs on the mixer as well. You’ll monitor through the mixer and direct its outputs to your Genelecs. An option without a mixer would be a Mackie Big Knob https://www.mackie.com/products/bigknob/. You plug the card output into the Big Knob and its output to the Genelecs. It allows you to pick various inputs and send to different outputs. You get very nice volume control and talkback to a studio or booth if you have one. But, again, I’d suggest a mixer as you have much more flexibility, especially if you have machine or mic inputs you want to direct to FCP for capturing.
John
MacPro 8-core 2.8GHz 8 GB RAM OS 10.5.5 QT7.5.5 Kona 3 Dual Cinema 23 ATI Radeon HD 3870
ATTO ExpressSAS R380 RAID Adapter, PDE Enclosure with 8-drive 6TB RAID 5
24″ TV-Logic Monitor
Final Cut Studio 2 (up to date)
Pro Tools HD w SYNC IO, Yamaha DM1000, Millennia Media HV-3C, Neumann U87, Schoeps Mk41 mics, Genelec Monitors, PrimaLT ISDN