MXL 990 Condenser Mic and Art Tube Preamp - what do I need?

Answer 1

Because the 990 is a condenser microphone, it needs power to function.  The tube MP can supply this power via the +48V phantom power button.  The power is supplied from the preamp over the XLR cable to the microphone at 48 Volts.  Without supplying phantom power, the mic will not work.

Answer 2

 You should have an audio interface that connects to your computer via USB or firewire and some sort of digital audio workstation (DAW) software for your computer as a minimum for recording.  The recording chain will look something like this:

mxl 990 -> ART tube MP -> Audio Interface -> Computer

I recommend using the balanced XLR output on the tube MP rather than the unbalanced TS connection.  It will prevent some of noise from effecting your signal.  Also, you need to realize that the point of the pre amp is to get the signal from mic level to line level; this means that the audio interface should not be further amplifying the signal but just routing in to the computer.

Good luck!