My last band would jam in headphones whenever my better half was home. We used my large mixer (Allen Heath MixWiz3 16:2) into a Behringer HA4700 headphone amp. That mixer is a luxury, and really any mixer with enough.
If the guitar player has a pedal like a Boss ME-25 then that can plug straight into a mixer. If not, he could get a Behringer GDI-21 pedal. It is not great sounding but it's a starting point. And for $40 what do you expect.
Here is the short list in links of what you will need at the least.
Mixer (look on Craigslist for a better mixer for less)
DI sim pedal(if needed)
Cable from drums to mixer
Then a couple of adapters for your headphones and you're off to the races.
Jamhub looks like a great product. I have no experience with it.