For the Oxygen 8 V2 you can use usb into the computer or a midi cable into your interface. Akai XR20 you will need 2 balanced instrument cables at the length accordingly to where you want the machine placed from the interface.These two cable should hook up to the interface channels 2-3. Blue Yeti Pro will connect through an XLR again at whatever distance you want. The XLR cable will go into channel 1 into your interface. As for an interface; You get what you pay for. Poop in poop out as the recording industry says. Unless you have a firewire input on your PC then you won't be able to use the Saffire Pro 24. If you do have firewire, Then that is a great deal. I spent $2,000 on my 4 channel interface.