Hi

If you look at the top of this page you'll see a link to Custom Tone.  That's where you will find a whole bunch of tones for your Spider IV 75

Yes - you connect the amp to the FBV MkII using the standard Ethernet cable and then you connect the FBV MkII to your computer.  You d/l the presets you want from Custom Tone or elsewhere and then you load them into the amp's editor software (Spider IV Edit) to audition the tones and if you like what you hear you can SEND the tone permananetly to your amp from the editor.

You do need to install your FBV MkII pedal board's drivers onto your computer and you should make sure your amp can be 'seen' by the computer.  You should use Line 6 Monkey to update your amp's firmware to the latest version if it isn't already - takes about ten minutes to complete the update.  If your amp's firmware version (shows up briefly in the amp's LCD when you turn it on) is less than 1.50 you must update it to be able to use the editor.

Nick