Yamaha DTXpress/DTXplorer/DTXtreme

Hi
I have had my DTXpress 2 for about 8 months and I'm finally wanting 
to delve into the world of PC connectivity. So my question is how do 
I do it?

I have read the tips on DTXpressions, but I dont have a MIDI 
soundcard. I was thinking about getting a USB/MIDI interface thing 
that M-Audio makes as this seems like a very simple solution to me 
not having a MIDI soundcard. 
Which of these MIDI interfaces should I buy, they do 1 in 1 out, 2 
in 2 out, 2 in 4 out, 4 in 4 out and 8 in 8 out. Im assuming i only 
need one of the smaller ones, but which one?

Thanks for any help

Will