Here's the chain I am using for recording my electric Les Paul guitar:

Guitar --> ARTcessories Zdirect (DI Box) --> PreSonus Firebox (audio interface)

I am using Native Instrument's Guitar Rig 4 as the processor.

The problem is whatever guitar settings I use in Guitar Rig, I get a low noise / hissing sound. Sometimes it sounds good and vintage but I just want a clean and neutral sound. What should I do?
Skip the DI. I don't see any need for it as the the Firebox already has mic/inst. ins.
ditch that DI box, no offense, but it sucks complete arse
5150 III 100W, Mesa 4x12 Cab, Framus Cobra Cab, M-Audio Profire 610, ISA One Pre, SC607-b, Equator D5's, Countryman Type 85 Di box, Radial JCR, Superior Drummer, SSD 4 Ex, TS9, NS-2 and the list goes on and on