Helix can do 4 outputs at once. 2 balanced 1/4 inch and 2 XLR. Can be mono or stereo. It is remarkably simple and powerful. The outputs can even have some with cab sims (IR) and without for occasions where there might be a signal to the PA with a cabinet sound, but the monitoring is an old fashioned amp and cab.
I would recommend a Technical Rehearsal or two as all PA systems are a bit different and his sounds might need a tweak. Sometimes it's as simple as changing the IR, sometimes it needs a bit more, but a few hours to just get the tones set will be well spent, especially making sure the monitoring works well for everyone.
One of the best bits about modern modelling units is their vast memory for sounds - so if you guys play some venues regularly he can actually save all the settings during the first soundcheck at a venue and name the patch(es) for that venue and just load them up again next visit. No need for a little black book anymore. The soundcheck process can get a lot faster.