Besides the computer, you need to consider your needs in a soundcard/mixer. Do you want to be able to mix ITB? If so, you need to consider something with enough inputs and outputs to accommodate your gear; furthermore ( and this can be the tricky part that requires really understanding the specs), a good majority of the devices out there that allow you to digitally record to the computer are only in stereo, especially with USB devices. If you want to multitrack, you want to make sure the device outputs each input in mono/stereo. Do you want to have the flexibility of recording the individual outputs from your Elektrons? Then you probably want an interface with 8 inputs or so.

After a few missteps, and much wailing and gnashing of teeth, I personally decided to get a Focusrite Saffire Pro 40, and a Presonus Digimax FS (connected via ADAT), giving me 16 mono/ 8 stereo inputs. I connect everything in stereo through a patchbay, and if I want to record from all 6 outs on the MD or MNM, it is as simple as just plugging a few cables into the patchbay. My outboard effects are connected to it as well, making it easy to patch in an effect when I need it without rerouting everything.

If you don’t need to go that route, a mixer with USB or FireWire should do just fine for you.