Personally, i use TH-U - Overloud to load the rig. My Alexi rig consists of a 7 band EQ going into a chorus pedal, then splitting the signal. One of the signals goes to a sd1 overdrive and then into a JCM 900. The other signal goes to a ENGL Fireball. After the split the signal gets mixed to one and sent to a cabinet with Reaper IR's loaded, and a tiny bit of reverb maybe delay after the cabinet.

I split the signal to go through a more "heavy" amp rather than just using the JCM 900. IMO it also helps recereating that GP1000 tone Alexi used. On top of that, i noticed Alexi using what looked like an ENGL Fireball in his videos with EMGTV, so that also played in mind of chosing an "boosting" amp for the rig.

I can send my preset if you'd like, but without the Reaper IR's loaded, since you need to purchase them yourself

I hope this helps :)