ive had a bunch of interfaces, the line6ux2 comes with some nice software, but what youre doing with one mic, any plugs can do....probably a expander/gate to remove room noise, some eq, comp and you'll get some good sounds.
You could save some and get a UX1, it has XLR for one mic.
had a M-Audio something too they are all in the same shelf of gear, and do amazingly well. Tascam 122, 144 etc..
the software(gearbox/podfarm) is fantastic it has all vocal preamps and comps and eqs, you'll need, and you can get more gain and clarity through this too to help with the units preamp.
But almost any DAW will have plugs too. You can get free gates and expanders, eq etc.. to get noises out of your takes.
if it's not happening in the room, it ain't gonna happen on tape.-HG