My suggestion, if you like your current 4 ohm cab, and you like the tone from the GK - buy another 4 ohm cab and a 1000W+ rackmount power amp that can do 4 ohms (or less!) per side. (If you’re ok with a heavy amp, plenty of old lead sleds out there in the used market. I used a QSC 1450RMX for a while - heavy, but gave me all the wattage I could need.)
You’ll just have to make sure the line out from the GK is the right signal strength to match the power amp’s input. And make sure you can “bridge” the INPUT to both channels of the amp. (Not talking about bridging the output!)