Loads of DI options as people have stated, Tech21 DP3x pedal is a massive winner for me, new Fender ‘multi Fx’ unit which has EQ compression and DI capabilities, Trickfish Trilobite, or even just a DI box and nothing before it, my radial JDI is great (and it has 2 inputs/outputs).
I agree with what the others have said about a load box, you guitarist can crank and keep the volume controlled. Two Notes do great ones (captor) and their cab sim Torpedo could work a treat for him.
Or if he likes new kit, Friedman have just released the JJ model either head or combo which was made alongside Jerry Cantrell of Alice in Chains, and that is 20w tubes with an internal load box, so you can just go straight out and have no speaker connected - it sounds bloody immense!