Ok, it was easier than I thought. A couple of YouTube videos recommend starting with the Cali IV Rythm 1 or Cali Texas Ch 2 amp and both YouTube videos recommend the Scream 808. Just both of these blocks along with a stereo reverb (Dynamic Hall) gets you pretty close to his sound with the right guitar. I'm using the settings below with a PRS Custom 24 with the pickup switch in the middle (both humbuckers). Pretty happy with the sound, but I would like to figure out how Santana gets that snap attack slap echo sound he gets around 1:28 in the YouTube video above. My guess is it might be more about technique and possibly the type of pick he uses.
Mesa Boogie Mark II C+ (Cali IV Rythm 1)
Drive - 9.4
Bass - 7
Mid - 7
Treb - 5
Presence - 7.1
Ch Vol - 5.1
Master -7
Sag, Ripple, Bias, Bias X - 5.0
80Hz +1.6 dB
240Hz -0.5 dB
750Hz 0.0 dB
2200Hz +0.1 dB
6600Hz +0.4 dB
Tube Screamer
Tone 4
Drive 6
Level 3
