I'm a little confused by the question, but I think the answer is that the 671 can supply phantom power, so use it. You could add an outboard power supply like a Denecke PS/2 to handle the phantom power, but there really isn't an advantage, and it's just another piece of gear to deal with. So I would say, running right into the 671 is THE way to go.
Whether you need the 20db pad, is a separate issue.