Alexi's Gear
Alexi and Roope both run a Rack mounted setup. That means there's no "head" like with most half stacks. Their own cabinets are Marshall JCM-800 4x12's with Celestion speakers, though they have been known to be "gear whores" and use the previous bands gear while on tour.
The Rack
Alexi's and Roope's racks are nearly identical. I will list the rack in the orer that it would be wired in.
ESP RV350-AL
Wireless transmitter (Most likely a Sennheiser, as they are the best right now)
Lee Jackson GP-1000 Tube preamp -
www.leejackson.com
Sans Amp PSA-1 Solid State Preamp -
http://www.sansamp.com/
Rocktron Intelifex Effects Unit -
www.rocktron.com (this particular unit is now discontinued, but it's available on Ebay)
A) Lee Jackson SP-1000 Power amp*
www.leejackson.com
B) Engl E840/50 Power amp*
www.englampsusa.com/ (USA)
http://www.engl-amps.com (Europe)
C) VHT 2/90/2 Power amp*
www.vhtamp.com
Marshall JCM 800 4x12 cabinets
www.marshallamps.com
*they use various power amps at different times.