nothing really. same amp. the SX was first and second generation. the XTR was what Orion changed the SX name to after giving the amps a facelift with rounded off cooling fins and the redesigned Orion logo.
thanks for the reply. so i would get full power out of it running at 4ohms mono right? i have a RE HC dual 2ohm vc. would this sub work to get full power out of this amp? thanks.
yup. I use two 2250SX amps bridged to drive a pair of dual 2 ohm coil triple X 12" subs myself. 1280wRMS @ 14.4VDC stock. a bit more with modified internals. nice amps. I'd kill to get my hands on 3 of the GS500 model amps.. heh that gold plating was pretty. I may have to look into plating costs for the 2250's