I am going to record some demo songsI have made, I have a Digitech GNX3, I plan on going straight from the SP/DIF output on there straignt into my SB Audigy 1 SP/DIF input. I have these softwares I am thinking about using but need input as the what is the best? to get the best sound

1) Guitar Tracks 3 PRO
2) Cakewalk Project 5
3) Propellerheads Reason 2.5 /Rewire

I heard Cakewalk was good but I cannot find out how to get the guitar to play thru in cakewalk, I cannot find a guitar setting or "instrument", its all snynths or bass, what do I select to get any input in Cakewalk from the guitar, I have the midi settings and Audio settings set up correct I think.
I have tried Guitar Tracks 3 but it keep lagging way bad, I have a Pentium IV with 512 megs ram and lots of HD space free, but th esounds lags bad and then it just quits sometimes

Thanks